I remember hearing the typical mixed review, they've helped some sites, but failed on a lot of others which is pretty typical in the business of ad management.
I'd say test small, and try and get net 30 terms so they can deliver some results first. This business is like most others, if you are REALLY that good at SEO and PPC, then why take pennies from other companies when you can run your own campaigns for millions of dollars?
What market are you looking for PPC help in? PM me if you'd rather.
Zeprokon