Not a fan. I have tried a couple shoulder rigs and the work for throwing on under a coat but sucks when you get somewhere and it starts to warm up.
My Dad shoulder carries most of the time under a button up. He hides his well but it is a small gun. It is the second slowest place (in terms of draw if under a shirt) to carry ahead of ankle carry.
IWB
OWB
Pocket
These above are more natural, faster and convienent. The only time I prefer shoulder is when riding motorcycles or quads.