This is one of the skinnier models on the market.  We needed it to fit across the back on a Toyota Camry as a spare seat for little friends.  It does the job fine.

Fabric insert is easy to remove and wash in the machine.  Whole unit is easy to clean, and it lives in the boot of the car most of the time, holding up to the wear and tear extremely well.

It has an adjustable guide strap for the car seatbelt to hook into to keep the seatbelt in the safest position for children.  On long trips we also use a H-strap, though.