We both wear R3 Rage restraints. I think if you use a suspension seat, under big impact it will still have the back board to restrict head movement even if the belts aren't as tight as normal. The back board doesn't bother us at all and you can adjust the amount of head movement. I don't think you should allow much movement for real safety even if it is nice to look side to side, not a good idea to me. We rolled at Glen Helen a few weeks ago and had no soreness period. Priced at around $700 is kind of in the middle of the price range for restraints. Just one racers opinion however, but that is what you asked for I guess.
I as the others on our team use the Leatt Brace. I can only compare it to the D-Cel and can honestly say it is a million times more comfortable and easier to race and work in. No restricted head rotation, I can change a tire with it on and no sore/tired neck! Thankfully I haven't had to put it to the ultimate test but if I do I have complete confidence in it.
x2 - Jeff hooked both my brother and I up with our R3's/ I have the Rage and my brother has the Hybrid. Both are the same size but they fit our bodies differently and the one we chose works best for us. The slip in pad with cutout works awesome in our Sparco Tub seats.