i know not buggy, but need quick maxicosi carseat help!

[fairimum]

my dd2 was 7 weeks prem and is now 9lb at 5 months. our cabriofix was in the car when dh had an accident and the insurance have offered to replace it with a pebble (think might need to argue if want a cabriofix), only downside i can see is the weight being slightly more - any other disadvantages? have you used both? which would you choose and why?? need to make a decision today so any help much appreciated!
thanks