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.
The guy at the parts house was so proud of his new item...demonstrating it to all. Then he did a demo for me- and bent the pipe a little too tightly, and couldn't get the spring out!
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.