Have you handled a Rada back? These were cheap and cheerful when they were made, I had a couple (for a 9x12 cm camera) and found the film was so slack it was being scratched by the sheath as this was pulled out. Total junk, which I binned without a moment's hesitation!
Interesting. I bought a 6.5x9 plate camera earlier in the year & it came with plate holders & a 120 rollfilm back. The film back has no brand name but it looks somewhat similar to the Rollex backs. It works well so I seem to have gotten lucky on that deal.
Goldie ... in the end I picked up two Rollex film backs, so I have one for the Vag and one for the Ideal (slight mod required).
Since I mostly use fast film I've had to blank off the red window and rely on counting my way through the frames. Works a treat, though it seems odd to roll the film backwards.