After spending so much money on development, they think the only way to get a return on the large investment is by charging a fee per download. There are lots of big players out there who are making lots of money. You can achieve this similar zpp as well if you follow a few very important monetization strategies. So your best choice is to offer or it without charging. Then try to get as many downloads as possible and look to other options for revenue streams. As an industry expert who mqkes been through this before, I can tell you from personal experience that it works.