I've winter carried in horizontal shoulder holster for years. It's one of my preferred carry methods, especially when I'm driving.
I've carried both revolvers and semi-autos ranging from small to rather large and heavy.
One big consideration if you're going to be carrying over long periods of time is to go with wider shoulder straps to distribute the weight.
I've gotten a fair amount of grief from different people over the years for carrying in a shoulder holster, in a horizontal shoulder holster, or both.
The biggest complaints from the naysayers are:
1. The muzzle's pointing at things you don't want to shoot!
2. When you draw, you're pointing the muzzle at your body parts!
Dealing with number one, no matter how you carry, your muzzle is going to be pointing at something you don't want to shoot.
Obviously the concern is that with a horizontal holster the muzzle is pointing at things/people behind you.
Frankly, I dismiss that concern because the gun is secured in a holster and none of my firearms have ever been possessed by demons that have decided to fire them randomly with no human interaction.
Naysayer argument number two is absolutely ludicrous. I can't think of a single CCW-type holster, or any other kind of holster, that doesn't result in the muzzle pointing at some region of your body when you draw.
Good evidence for that can be found in the Utoob video of the guy drawing a .45 Colt from a belt holster and sending a round through his leg.
The cure for that?
KEEP YOUR DAMNED FINGER OFF THE TRIGGER WHEN YOU'RE DRAWING YOUR GUN!
Speaking of fingers and triggers, that's been an argument against the Sherpa holster. Recently one of the friends of the Sherpa, a highly experienced gun guy, decided to video himself drawing from the holster to prove to the detractors that the finger didn't go anywhere near the trigger on draw.
Guess what happened... Video clearly showed his trigger finger hard on the trigger during the draw.
So, whatever holster design you decide on, make sure that it's one that allows you to keep your finger off the trigger during the draw.