@Wawawuh: how would you be hanging? If you are hanging light, like 5-6 pounds max, then the lighter springs would be OK and compliment the hanging nicely. Although I’ve never seen extender springs which produce over six pounds of force so the heavy springs should work as well, perhaps better in the long run.
The springs are rated at 5.5 lbs. I’m assuming that means 5.5 lbs of max force they will apply. I can only where the extender for like an hour at a time with these heavier springs before I need a break to just get the blood flowing and relieve the pressure near where the base of the extender is pressing into the pubic area. With the light springs I can leave the extender on for hours at a time.
I think I’ll try vac extender at 7.5 lbs for two sets of 30 minutes twice a day, each followed by a light 50 rep set of jelqing then 1 hour of the extender with the heavy springs. I’m at 5.8” BPEL now and will measure again in a few months to see if I’m making good progress.