Actually, you will need a lot more than 10 pocket dipes. You need a pocket for each diaper not each cover so if you think 24 dipes is a good number you need 24 pockets.
I think they say it's cheaper because you can leave you baby longer without changing them. Personally, I think that's gross and I want to change my baby as soon as she's wet. I think that if you want economical prefolds and wraps can't be beat.

