Hi Warren,
I have never seen the blue and red striped belts, or even the horizon blue ones in any photo, all of the Nieuport 11/16/17 interior photos (which are black and white of course) seem to have the narrower belts with large leather pad where the buckles are, these would be #3 and #4 in the first link you showed. I have not seen the wide belts that Eduard gives you, but would have to guess these were for early aircraft or 2 seaters maybe.
As far as bending the prepainted belts, I have done like Rick does, bend them up quite a bit before gluing them in place to give them a lot of wrinkles, then attach them with acc to the seat cushion, then bend over the seat and apply some more glue to the side to hold it down. The Eduard belts are very thin and I used them on the 1/48 Fokker D.VII and Albatros D.III OEF with good results, no annealing required. The paint they use seems to be flexible and sticks well to the metal when bent, but I'm sure it would blacken and peel off if heated up.
I have not seen the Super Fabric belts yet, but bought the cloth belts for the SSW D.III, just have not got around to using them yet. The vinyl flat surface does not ound like a better alternative to the photoetched prepainted belts, especially if they are vinyl, in that case you will not be able to bend them to get realistic creases.
Dave C