Can't keep SA FW rays in my state, but I have kept Oxydoras niger before and they were a great fish. I started with one about 10" and it outgrew a 135 over time. It loved coming to the top for cichlid sticks food and was very tame. When it got too big for the tank, I took it to an indoor koi pond in a hotel where it grew to a huge 3' in length. It looked rather like a big black shark as it cruised around the pond! Later I got a second one and after a time did the same with it. The two lived with the koi for a long time but I think they finally died a few years ago. I have never known them to bother or eat even small fish and there were thousands of guppies in the pond with them and the koi.
At some point I want to set up a large (300 gal. or so) SA tank and this will definitely be one fish I will be looking for again. If you have the room I highly recommend them!
