We just bought a Mazda5 through Rent2Buy (still haven't gotten back our title and registration, but signed the purchase agreement so it's "ours" at this point) and I thought I'd report back.

Some notes:

• One quirk is that they don't guarantee the car will actually be available at the reserved time, since it's an active rental vehicle up until the moment you decide to keep it and could get returned late or to the wrong location or whatever.
• The HLE location in the 'burbs where I reserved mine was happy to pick me up from the train station a mile away.
• To answer my own earlier question, there isn't really any way to determine details about the car beyond what's on the website. The Rent2Buy people know nothing and the pickup location probably won't have the car until a day or so before you're scheduled to pick up. They DO, however, allow you to return the car without any charge within 2 hours of pickup if you don't like it.
• An individual can only hold one Rent2Buy reservation at a time. So you can't reserve several cars and then take the one you like best when you show up (although I guess spouses could make two reservations). Also, because you have to reserve at least a couple days in advance, if you're really picky it might take several weeks of rejecting cars before you find one you like.

We're not that picky, though, and were fine with the first one we tried. It was the color we wanted, had reasonable mileage (about 34k) and was a couple thousand cheaper than anything I could find through conventional used car channels (many of which had Carfaxes indicating they were also former rental fleet cars).

As soon as I picked it up I drove straight to a mechanic who put it up on a lift, checked the computer and generally poked and prodded and declared it in decent condition. Yes, it has a couple little dings on the doors and some scratches on the bumpers, but we're going to be keeping it in Manhattan (sometimes on the street) where it's bound to get dings and scratches anyway.

The only unpleasant surprise so far has been the cost and hassle of getting additional keys. The rent2buy site said it would only come with one key, and I learned after I bought it that if you have less than 2 keys you HAVE to go to the dealer to get a second key (and to reset the codes for the whole system). I imagine anybody who has owned a car in the last 10 years would know this, but my last car was a hand-me-down my parents bought 25 years ago.