I just bought a Radian for my son. The only difficult part of the installation for me was the tether. It took a while to figure out how to install it because our seats are electric and there was not a D ring anywhere in sight. We just had to remove a plastic piece that was covering the foot of the front passenger seat so that we could hook up the tether correctly.
I like the radian a lot, and though parts of the installation were difficult to figure out I would buy it again in a heartbeat. I do need to mention though that I only bought one so that I could see if it would fit in our car as well (Audi A4) and it really does not fit in the Audi at all. I have it in our Silverado pickup and it works wonderfully there.