I've only started to look. From what I recall, the Clek rates as better in CR crash test safety while the Nuna is good. There are also various other organizations that provide crash test ratings. I haven't decided if a better crash test rating is more important than for example a seat that works as a system with whatever stroller I choose.
I've seen the manufacturer's crash testing for both of these seats. If you have it installed correctly with the load leg in use, both hardly move at all, meaning very few crash forces go to the child. The 3rd party ratings you may see don't give the whole picture. They only test a seat 1-2 times, while the manufacturer has to test it over 50 times at a minimum, but usually over 100. The 3rd party testers also tend to leave out how they installed the seat, what size dummy was used, and how the crash testing was conducted.
In the European/UK market, the nuna seats are infamous for poor fit and head flop in small babies. The best fit would be in something like an avionaut pixel pro over here.
The comparison slide says that the Nuna Pipa RX contains flame retardant fabrics in "all colors," meanwhile their site states: "From fabric to foam and beyond, each element is smartly sourced to be both flame resistant and contain no added fire retardant chemicals" and "PIPA rx is fashioned solely from materials that are free of fire retardant additives" - just confirming that "Flame retardant fabrics" here means "no added flame retardant chemicals" or "naturally flame retardant fabrics" and not what I inferred it to mean which is that chemicals were added. Thanks!
