It's been a long time since I've worn a shoulder holster. I have tried a few that just didn't cut it. One of my problems is I am heavy. Most heavy people aren't comfortable with a shoulder holster unless they buy from a company that knows what they are doing or the rig is custom fitted.
The best shoulder holster I ever used was an old Jackass model. They are being made by Galco as the "Miami Classic" these days. Itwas a vey comfortable holster for me. I did modify the mag pouches so that they hung horizontally instead of vertically. This made it much easier for me to get the spare mags out.
Anyway, cheap won't get the job done if you are serious about carrying all day.