Underdrive pulley's

Has anyone tried these yet?
http://store.summitracing.com/partdetail.asp?part=ASP-541084
For 30 minutes of work you get up to 15 horses and that's less than $100. Sound too good to be true. I might get a set and a new serpentine belt to go with it. Would this not be good for a daily driver?

It really only frees up HP by turning the accessories slower.  So you may not get the performance out of your alternator for the charging system (ie. bad for high current drawing applications - stereo, extra lights, etc), water pump & fan (may not be good if you live in a hot climate), power steering pump (probably won't matter much), and your A/C system may not have the output that it would at normal speed, but again, if you live in a hot climate, you may need that A/C performance.