Are these okay? - 48cc bicycle motors

I found an ad on ebay -
http://cgi.ebay.com/48cc-SCOOTER-KIT...QQcmdZViewItem
for a bicycle motor kit. I understand you have to pedal a couple times
from a stop, and then engage the clutch on the handle bar. (And start
it the same way, but while going faster.)

Do these work okay? Once going, will it take the bike up hill? (city
street)

There are a couple other places selling similiar kits under different
brand names.

Thanks for any comments or experiences.