Radiant Barrier
As a former Custom Home Builder, I was, and am still, a believer in radiant barrier. We used the radiant barrier applied roof decking twenty years ago. What it does is not allow some of the suns radiation to penetrate to the attic side. If you don’t have a foamed attic, I would at least want a radiant barrier. We do not install radiant barriers.
As for the sprayed on radiant barriers, it would be hard to justify the expense. The only way to quantify the actual benefit would be to get attic air temperature readings before and after on identical days.
However the major flaw has still been ignored. The flow of air through your attic is robbing you all day, everyday, of your energy dollars. Leakage is the big thief of your utilities; you have to stop the leakage which is a big reason for the effectiveness of foam.
(See R-Value vs. Air seal)