As for my opinion I love it over the Britax b/c the bottom of the seat is lower. DD's legs don't fall asleep like they did in the Britax and the seat is easy to get on and off an airplane and travel with. It also makes it much easier for dd to get in and out of. It's convertible although we didn't need it to be. And cheaper than Britax. At least for now.
I love our Radians. They were $50 cheaper each than the Britax that goes to 65 lbs, the girls are very comfortable, I can get them in tight quickly which is important since I use my mom's car. I haven't used them rear facing (baby is still RF but in the evenflo) but I have been very happy with them FF and I am thinking of turning the girls back around if they will let me (they are only 24 & 28lbs)