A vendor held
mortgage is usually preferable to rent to own. With many such arrangements, you can get screwed. There are often bump off clauses where the owner can send you packing if the value rises and you haven't saved
enough to match whatever has been offered.
I used to
sell real estate in Ontario. Most rent to own negotiations go nowhere. I never put one together.
Rent to own, often let's the owner play the market when things rise. When prices drop, renters may stay since they have invested time and money and they tend to be people of limited options and means. It could work, or it could be one step above sharecropping.
An agreement of purchase and sale, is not an ambiguous document. If you're taking the plunge, protect yourselves.