As soon as I took my first pedal stroke on PowerCranks I realized that it was going to be difficult to manage even 30 minutes on them. Even clipping in is weird as you have to clip in with both pedals at the 6 o' clock position, and standing is also really different and takes some time getting used to. It turned out that I rode 1:10 and was really tired after that, but suprisingly I wasn't that sore the next day.If you've ever implimented one legged pedaling into your training, PowerCranks are very similiar except you're doing it with both legs at once. Your first time with them you'll be able to ride 30 or so minutes at least, and it will probably take so much concentration to maintain a good stroke that you probably shouldn't ride on heavily trafficked roads.
According to PowerCranks you could see improvements in as little as 2 weeks. Unfortunately I've only used them a couple of times so I can't verify that claim. However, although there seems to be a lot of benefits of using them, PowerCranks are heavy (although I guess that would only make you stronger), and the cheapest model is worth $899.
You can go to http://www.powercranks.com/ for more info, including testimonials by pros, coaches and amateurs alike.
All in all, PowerCranks are pretty cool and I'm definitely looking forward to using them as an off season training tool.
