The first is that it wasn't designed to be a disc cart like the Delta Cart. The second is the axle. There's so much axle on either side of the RR that I'm a bit worried about it bending with my big ass sitting on it regularly. Couple that with a pretty small warranty (in terms of disc golf generally seeing a lifetime warranty for bags), and I'm more worried. The thing that really bothers me the most though is the disc frame. PVC just screams DIY cheap. It was one of the reasons I went with an aluminum framed Ergo over the Simian for a backpack. I'm sure it won't be cracking or sagging for years, but it's the material of choice for the DIY crew, myself included. On the plus side, any cracking or sagging pieces are easily replaced.
My biggest complaint on the Delta Cart is the use of velcro to secure the lid. I'm buying a cart to have for the foreseeable future, and velcro and I just don't get along. It wears out pretty fast for me. That's a small complaint though since it looks like I can replace the pieces pretty easily as needed.
That's not to say that the Ridge Roller isn't a great design that'll give you years of enjoyment. Because I'm souring on the Delta owners' lack of communication, the RR is truly looking like the better choice right now. I don't think either are perfect, but I do feel like the fit and finish, at this time from pics and videos, is better on the Delta.