To try and save you the trouble of a search, here's a synopsis: Some (even the very highly educated) people think they are malarky. Some people think they might work, but aren't convinced. A very small smattering of people have even tried them for a very short while, gave up (for various reasons...too hard to ride, afraid it will take away from their "normal" training, etc.). Other people think they might work, but they're too expensive, or they'd rather spend their alotted money on race wheels, etc.
Then, there's another group of riders: those that have actually trained on them. This is the group that overwhelmingly thinks they are beneficial, if you do the work they require in order to improve. This group is split into two main camps...those that think they should be ridden all the time, and those that think they should be ridden only part of the time.
I'm not a runner. Well, I used to be a decent sprinter a few decades ago, but, I've never been a good endurance runner. I've never heard anyone (in the group that has actually used them) that says they didn't help on the run. I'm referring to people that previously ran 30 minute 5K's, as well as people that previously ran sub-20 minute 5K's. I went from running 24-25 minute 5K's in triathlons to 21-22 minute 5K's in the same triathlons, AND increasing my bike speed in these same races (on the same courses as last year) by a couple of mph. Alas, my swimming hasn't improved...that's my only complaint about PowerCranks.
I've had mine since December 20th, 2002. I just did a sprint triathlon this past Saturday, I was 5th in my age group, last two years I was MOP. I did my first 1/2 iron distance a month ago, I was 4th in my AG (39th fastest run split out of 300+ males) on a day that over 40 people were put in the hospital for heat-related illness. A week before that race I was 2nd in a Duathlon. The first triathlon this year I was 4th, the last two years I was MOP in the same event. In April, I ran a half marathon (the second of my life) and hurt my achilles at mile two (later found out it was due to a bad heel-counter in my shoe), but I kept going, limping along, and still ended up 7th in my AG with a 1:37...and I hadn't been running much....just PowerCranking. No way would I have been able to do this without the stronger hip flexors that I'd developed by using PowerCranks.
Are the claims made on the website true? It depends on the individual. They accurately reflect what I am personally experiencing. I've picked up over 2 mph so far on my bike splits over last year (on the same courses), while running a couple of minutes faster in 5K's. I still have yet to be able to attend our local 10 mile TT to get a pure TT speed reading (last year my best was 24.9 mph)...I'm thinking this year will be close to 26 mph...but I'll have to get out there and do it before I'll know for certain.
Yesterday, as a recovery day from the race on Saturday, I rode my PowerCranks for 45 miles...didn't feel too bad at all. I've come a long way from struggling to ride them for 20 miles when I was fresh. I'm glad I stuck with them.
Talk to people that have actually TRAINED on them, the rest know very little about PowerCranks as they relate to "real world" performance, in spite of some of them claiming to know much more about almost EVERYTHING physiology-related than the dummies that actually TRAIN on them. One person even stated that in graduate school they were taught to read only the results of a study and to make up their own mind as to what the results mean, without regard to the author's own discussion about the potential problems in obtaining and interpreting the results. That's fine and dandy. But, in Kindergarten, I was taught that actions speak louder than words.
Performance gains are what we're after. Words don't make you faster.
The only way you'll know if they help YOU is to try them out. Otherwise, it's just academic onanism to discuss them.
Good luck with your decision. Either way, it's not about life or death. You CAN improve without them, no doubt. But if you've hit a performance plateau, make sure you do something other than what you've always done...because it's crazy to do the same old things and expect a different result.
Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)