I've not seen these springs. Small PVC seems to bend just fine for me with a regular hand EMT bender. Sure, it springs back, and you've got to take a couple of shots for a 90°, but it saves carrying yet another tool, and actually works quite well.
Another useless idea was; pack the tube with sand, or a molten lead fill for iron pipe, then bend it over your knee. Or the apprentices's head for larger rads. Oh, how we all laughed as we waited in out-patients for Doc to arrive from the Golf Club.