There was quite a discussion on these guys on a graphics forum I'm a member of.
The problem with them, is they are not paying for the rights to rent those dvds to others. They are making copies of dvds they purchase, and then "renting" those out.
You'll notice in their "how it works" section they even mention they are going to send you a dvd-r.
The problem with this model, is that the person who authored the videos aren't receiving any form of royalty on the products being rented. Videos rented from your local rental store are especially packaged and marketed for rental. In other words, they cost a lot more to buy, because of the renting aspect.
All depends on how you feel on the issue. Personally I have a hard time supporting a website that tries to go around the authors of the videos.
- Noel