the coupe has the anchor points and the roadster doesnt
just my opinion as a firefighter dealing with and specializing in rtcs the last 11 years,
a forward facing seat like the recaro is as safe as you can be with your child in the z coupe(and what i use)this is down to the fact that with the seat back full and the recaro installed, the dead space between the airbag and the seat is greater than the deployment range of the airbag,however NEVER fit a rear facing seat in these cars if you value your child.