worth it if you have lots of 1-2 handed downtime at work or home
I used this thing and the stiffer 40lb? resistance one. I ended up favoring the harder resistance anytime I only had a single hand, but whenever I had 2 free hands I'd use both and alternate as one arm became pumped from the extra resistance.
Overall very functional, smells likea rubber doggy toy, people WILL think it's a rubber doggie toy, and it works for finger and forearm strength.
My only gripe is that after about 3 months of consistant use (mostly at work 8-5pm) the harder resistance ring snapped in half . . . which was a bummer. I still have the lower resistance ring and use it to warm up when heading out to a climb, better then warming up on your first lead of the day ;)
Worth trying, but takes some getting used to (use fingertips) with the positioning. Less technical than other alternatives, but it won't last forever if you actually use it.