Power Cranks?

I have a set that I've had for about a year (and which I'm selling, BTW, with chainrings and BB). Do they help? Yes. What they do is allow each crank-arm to work indepentently, meaning that pusing down on one crank arm does NOT raise the other one. You have to lift it yourself. Much like doing one-legged drills continuously.

I found them to be GREAT for warm-ups before runs.  I never took them out on the road -- I used them on a trainer. Even in the little time I used them (probably 10 hours total), I did notice a difference.

I'll freely admit that I didn't give them the "fair shake" that Frank Day says they need (and you can call me lazy). I'm not saying anything against them. I just had to take the trainer bike and convert it to a commuter, so I don't have a hard-tail bike that I can take out of the stable for PC use (Softrides just aren't the thing with PC's, in my opinion).

Yes, they can be used in a race. There's nothing illegal about doing so. DEFINITELY give them a lot of time before doing so, however.

My friend that has been doing Tri's for over 20 years and did Kona twice, with his last one being last Fall, absolutely loves them.  He has noticed quite the improvement on his leg strength.  He showed me his set that he has on his mountain bike.  They independently allow you to work on one leg, or do "bunny" workouts, have both legs pedal the same motion at the same time, unlike the traditional cranks where one goes up as the other is going down.  It would take getting used to, for sure.  They are also not cheap in price.