In a nutshell

A comfortable, user-friendly car seat that offers above-average safety protection and should last for years

What we tested

  • Ease of installing
    A star rating of 5.0 out of 5.
  • Comfort
    A star rating of 5.0 out of 5.
  • Safety features
    A star rating of 5.0 out of 5.
  • Style
    A star rating of 3.5 out of 5.
  • Durability
    A star rating of 5.0 out of 5.
  • Worth the money
    A star rating of 4.0 out of 5.
Overall Rating
A star rating of 4.6 out of 5.


  • Sturdy, great safety credentials, comfortable, grows with child, easy to install


  • Could be a tad lighter in weight

Britax Römer Kidfix III M is the latest version of the German-British brand’s popular Kidfix range of booster seats. A Group 2/3 car seat, it is tested for kids from 15-36kg, so will last several years, from around 3 years to 12. (Although I would keep my preschooler in a harness and rear-facing for as long as possible.)


It is more expensive than cheaper and more basic models, such as Maxi-Cosi’s Rodi series or the Joie Trillo and Duallo models. However, it offers an array of safety features such as SecureGuard to help keep the lap belt in place, and additional side impact protection (SICT).

Other car seats that offer similar safety features include the BeSafe iZi Flex FIX i-Size, which is the first to adhere to new i-Size testing and costs £249.99, and the Cybex Solution Q-Fix, which is £190.

Tested by:

Anna tested the Britax Römer Kidfix III M with her tall five-year-old daughter on both long and short journeys. They liked it so much the seat is now used on a permanent basis.

First impressions of the Britax Römer Kidfix III M?

When I unpacked the Kidfix III M, it felt sturdy, durable, simple and well-made. I was sent the black version, which is fine by me – I’m not one for over-designed car seats. Function is definitely better than style in this instance.

What age child should go in a Group 2/3 car seat?

A group 2/3 car seat is a high-backed booster, officially suitable for kids from 15-36kg, which is approximately from 3.5 to 12 years. However, 3.5 years is still quite young, and I personally like my kids to face rearward with a harness for as long as possible, so I only started using a high-backed booster just before my daughter turned 5 – and only because she is very tall.

Is the Britax Römer Kidfix III M seat easy to install?

Like other parents, I found the Kidfix III M extremely easy to install. It is intuitive, with clear guides, and it has Isofix connectors that you can use to anchor your seat in the car. It can be used with or without these connectors, which is great if you want to use the car seat in an unfamiliar car, such as a hire car on holiday. Whether using Isofix or not, to use this booster correctly, you need to use the car’s seat belt as it holds the child and seat in place.


Does it feel secure once in place?

Thanks to the Isofix connectors and the back, which adjusts slightly to different angles of car seat backs, I achieved a great fit in my car. It felt very secure, with not much give in the seat.

Does the Britax Römer Kidfix III M car seat feel sturdy?

The Kidfix III M feels lovely and sturdy. The SecureGuard is nicely padded, and the fabric also feels good quality.

What safety features does the Britax Römer Kidfix III M have?

The Kidfix III M has some great safety features including the SecureGuard, which helps you position the lap belt securely over your child’s pelvic bone. I really like this feature – it helps with the transition from toddler to booster seat, as it takes the guesswork out of the seatbelt fastening. The car seat also has additional side impact protection, which you twist out of the seat on the side of the car door. This adds a great extra level of safety and reassurance. The seat’s safety credentials were also given the thumbs-up by other parents.



Is it easy to strap your child into the car seat?

It is very easy to guide the seat belt around your child, but it will always be a bit fiddly finding the seat belt connector to click the seat belt in place. I find this with all high-back boosters I have tried, as I need to lean over my daughter to connect it. It’s great that the guides of the Kidfix III M are so straightforward, and I loved the SecureGuard that helps you position the lap belt correctly, anchoring it between your child’s legs at the right position.

What do you think of the size of the Britax Römer Kidfix III M car seat?

I think the seat is reassuringly chunky and it protects the child well. At this stage, I wouldn’t want anything flimsier. Having said that, it wouldn’t work with all models, or for those who need three seats in a row.

How heavy is the car seat?

At 7.5kg, the Kidfix III M is on the heavier side for a booster seat, but it doesn’t seem that bad to lift and move around – a point backed up other parents, including those we surveyed*. There are much lighter boosters on the market, but I think the weight is manageable and it wouldn’t prevent me from taking it on holiday to use in hire cars.


Will your child fit in it until they are 12 years old (36kg)?

I would trust the seat to keep a 36kg child secure, and it feels like it would last a while as the seat is so adjustable. The extended seated area is also specifically designed to make it comfortable for older kids, so I think we will have a few more years with this seat.

How comfortable is the Britax Römer Kidfix III M for your child?

My daughter was very comfortable in the Kidfix. It seems a good size for her, and her legs were well supported. She even fell asleep after an exhausting morning one day, which she rarely does, and her head was well supported when she did. Plenty of parents, including those surveyed, also praised the seat’s comfort factor.


How many positions does the headrest have?

The headrest extends from 67cm to 85cm, so there is a lot of room for adjustment as your child grows.


Is the Britax Römer Kidfix III M easy to clean?

Yes, the cover is definitely easy to remove – more so than with other seats I have tested. I would be happy taking this off and refitting as needed, and so would parents we surveyed.

What do you think of the design?

The design doesn’t stand out, but it is solid and sleek. It comes in some nice colours, including a bright ‘Fire Red’, as well as a more bold ‘Letters’ print, so I’m sure you can find a style that suits you. I also liked that the extra side impact protection is extendable – you can easily twist it out, or twist it back in place for transit. You always need to have it extended at the car-door side for extra safety.


Are there any accessories available?

You can buy a spare cover and a summer cover.

Who is this car seat best for?

This is a great final car seat for any child. It makes the transition from harnessed seat to booster much easier and straight-forward.

Is the Britax Römer Kidfix III M value for money?

With an RRP of £180, the Kidfix III M sits somewhere in the middle of the market for this product type. Considering that you get superior side impact protection and a super-easy and safe-to-use car seat, with the option of an Isofix connection, I think it’s worth its price tag. It will last a number of years, so I think it’s great value – and plenty of other parents agree.

Would you recommend this car seat?

Yes, I would definitely recommend it. My daughter will be in it until she’s a teenager!

Where can I buy the Britax Römer Kidfix III M?

The car seat is available from Uber Kids and Buggybaby.

MadeForMums verdict:

A great car seat that provides fantastic safety features and excellent comfort for your growing child. It will see your preschooler through to their teens, and we will happily use ours for a number of years.

* MFM survey December 2019 of 564 users



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Product Specifications

Suitable for
Child age (approx)3 years to 12 years – approx
Child weight15kg to 36kg
Dimensions & Weight
iSize compliantNo
Car seat installationSeat belt
Removeable cover for washingYes
Side crash protectionYes
Recline positionsNone
Height adjustible headrestYes
  • Highback booster protection
  • Removable machine washable cover 
  • Ergonomic seating
  • SecureGuard
  • Side impact protection
  • Adjustable headrest
  • Adjustable backrest