Even if you did come out ahead, it wouldn't be by much. You'd be buying an overpriced property that the seller couldn't sell any other way except to someone with bad credit and while you'd feel like you were "buying your own home," when the time came to actually make the purchase you'd likely find that:
1) you don't qualify for the loan and the premium you paid to "rent to own" is money down the drain,
2) you do qualify for a loan and you realize how many more purchase options you have, except that you've invest so much into holding your "position" with the rent-to-own,
3) the seller goes sideways and either loses the property or sells it out from under you.
There are probably more pitfalls, but you get the picture.