Marketing Healthcare iPad/iPhone products - Free product supporting larger product

I have recently finished a contract for a health and wellness application for iPad/iPhone.  We have managed to become the #1 grossing app in it's category several times since it's launch over a week ago. 

The question I pose is if anyone has experience in iPhone/iPad marketing with respect to offering free applications to help promote a larger product.  If you have, what is the effect of this on sales?

Thanks for your time.

Dave