Hi icklekid
The Britax Baby Safe Sleeper is a good Group 0 car seat. It fit's sideways, rather than rear facing and as such allows baby to lie flat, safely. As it is lie flat it is better for babies spine and breathing, particularly if you make long journeys as there is no time constraint on lie flat seats. In an impact the way the seat is fitted gives baby 360* protection and the handle acts as a roll cage.
These seats are very good for tiny or premature babies, and of course parents who make regular long journeys. A few things to note is that the seat takes up two spaces in the car, and the seat is very heavy which makes it more cumbersome than an infant carrier if you choose to move it out of the car regularly. Group 0 seats won't last as long as a group 0+ seat, however they can be more versatile.
Kat
Good Egg Safety.