I'm not sure if I'd get a Radiation Vest if I didn't have one of the Radiation Jackets. The full liner is nice, but can get a bit warm. The vest is a nice compromoise. It does not fit as well as the full liner. The zipper is a bit longer and there isn't the loop to attach the vest to the jacket like on the liner. I just used it on a 45 degree day with 20 mph winds. The full liner would've been too warm. I had the vents open on the jacket, but had the jacket zipped most of the way up. I was comfortable.
BTW, I would not use the vest as an outer layer. I am still not convinced of the durability when not protected by a shell/jacket. So, I'd ignore the part in the description above about the "shiny reflective material aids in making you more visible" - especially since that's the inside of the vest/jacket reflecting warmth inward.