I had one for about 3 months (previous camera was a 5D3 which I had been very pleased with ). I only do low level, mainly Loop photography and knew when I bought it I was taking gamble, but after heaven knows how many hundred Loop visits, I'd got just about every shot and angle I could want and the prospect of different angles and pixel peeping offered by the 5DSR appealed. Also a couple of other togs whose photography I respect had used one and had got good results.
Didn't really use it a great deal in the Loop due to the poor weather when I had it, but was pleased with the results I got. I say pleased as opposed to very pleased because in order to try and keep images sharp with the 50mp sensor I was uppping the speed to 1/1600 from my normal 1/1250, also quite often I used th medium RAW mode (which from memory was about 30mp), also the frame rate was marginally limiting, although not massively so.
In the end I traded it in for a 5D mk4 which seemed to offer the advantage of an increase resolution and frame rate - and I had a trip to Rainbow lined up and didn't want to be worrying about which RAW mode and speed to use and screw up a F35 pass (I wish!). I can say that I am very, very pleased with the MK 4- although it expensive .
PS I think the first half of my Fllckr page (https://www.flickr.com/photos/47977048@N08/) are all taken with the 5DSR if you want an idea of what it can do.