My dachshund is on the Hills s/d at the moment... it only comes in the tinned stuff and I was a bit worried as she was on dried food before. However despite looking a bit vile (white lard like) she seems to love it. All the Hills prescription diets have got a fantastic reputation... the only down side I can see is the price. The Hills s/d works out at about £1.75 a tin.
I can't advise you on j/d, but like g_g says, they are great foods. I always have Hills i/d in the house for when mine has eated something she shouldn't. And my last dog who had kidney failure used Hills k/d.