Britax One4Life Slim

This seat has one of the tallest harness heights available as it goes up to 19.” Most car seats on the market have 17-18″ harness heights. If you have a child who is higher percentile for height, this could be a good option to consider.

It’s hard to find a seat that has a seat belt installation easier than the ones that feature Britax’s ClickTight technology like the Britax One4Life Slim does. The ClickTight panel is located under the padding. After opening it up, all you have to do is thread the vehicle seatbelt through the correct belt path, buckle it in, gently remove any obvious slack, and close the ClickTight panel. Note that the ClickTight panel is designed to be used with the vehicle seatbelt. Don’t even bother with a lower anchor installation; a seatbelt is the way to go for this seat!

This seat has a seat belt lock-off. So it can be a good option in vehicles older than 1996 that don’t have locking seat belts or need to be installed in international vehicles.

The Britax One4Life Slim is 17.5" wide,  making it a much better option for three across than its  19.5" wide predecessor, Britax One4Life! However, I still found it tricky to achieve three across with this seat in my vehicle, a 2012 Toyota Camry. After trying many combinations of seats, I was successful with an infant seat behind the driver, the One4Life Slim rear-facing in the center seat, and a Safety 1st Crosstown Slim rear or forward-facing behind the driver. To make this scenario work, the infant seat had to have a lock-off, be 17" or less in width, and be pulled as close to the door as possible. You'll notice we also did not use the cup holders for this seat. 

If your vehicle has non-removable headrests, we recommend using caution when considering the Britax One4Life Slim. It may not be compatible in the forward-facing and booster modes. However, we were able to fit it in a Toyota Corolla that has non-removable headrests. You can check this post for car seat options that do work with non-removable headrests. 

The seat is on the narrower side, so some older kids may find it uncomfortable. For reference, we have a 10-year-old who has a tall and skinny build. She found the highback booster seat mode comfortable. She is far below the maximum limits for the booster mode at only 53" and 53 pounds, and as you can see, there is not any extra room width-wise. 

The top tether should always be used when a child is forward-facing. Britax’s top tethers straps are v-shaped instead of the typical top tether design. Generally this kind of top tether will go around both sides of the vehicle’s headrest.

Our model is 8 months old. She weighs 17.2 lbs and is 26.5 inches tall. We tried her with and without the infant inserts since she is below the 20 lbs max for those. With the bottom insert in use, we had to move the crotch buckle out to the furthest slot, but it was still quite short. She fit best without any of the 3 inserts in use, and we moved the crotch buckle to the middle slot. She had no complaints about the comfort level either!