MI's & agt's posts are chock full of goodness. I'l try not to repeat.
https://thefiringline.com/forums/showpost.php?p=6395354&postcount=15
https://thefiringline.com/forums/showpost.php?p=6397583&postcount=25
I own a Galco Miami Classic II for my 1911s (GM carried most) and a Galco VHS for my 4" bbl S&W 629. And a M9 tanker holster for my GM 1911. MCII is a horizontal shoulder holster. VHS, is a vertical shoulder holster. M9 is more a chest holster.
Relative to belt holsters, SHs are slower, less comfy, good ones are less common, and more difficult to adjust to using. And you can't use them in IDPA.
That said, I own and use them when they are the best solution.
The Galcos are of good, not great quality. The M9 Tanker is of mediocre quality, but the design is solid. Were I to use the M9 more often, I would invest in one made by El Paso Saddlery. If a SH were my primary, rather than a secondary carry method for me, I would invest in a top of the line SH, not a Galco.
With a SH adjustment is king. And small adjustments make a big difference. Take the time to get it right. Then you'll wear it and find it is not right. Repeat until it is wear-able all day with comfort.
SH are the hottest, nastiest dadgum way to pack heat in the heat and humidity. No way I would wear one in Miami year round, that would be a near-constant heat rash. Same thing out in the woods if it is hot.
That said, I can get away with only a Dickies work shirt as a cover garment. Decently heavy material and dark colors help. Still too hot for summer carry south of the M-D line. Get it a size or two larger and keep it unbuttoned. One step up in cover garment weight is a sport coat or a denim jacket.
The longer the barrel, the more attractive is vertical carry relative to a horizontal carry. Prime example is a 4" N-frame S&W. Suckers are heavy and harder to pack on a belt than a GM 1911. I am big enough to conceal a GM 1911 in a horizontal holster. Not everyone has the bulk to manage that.
No matter what you see in Hollywierd, do not dual-carry Deagles in a SH for the love of Pete.
The M9 Tanker holster is tops for physical activity, as it is out of the way.
Belt stays/loops/thingys are a nice option to keep a SH from flopping about while upright and prevent the gun & ammo from flopping forward as much if you bend forward and don't use your legs as you ought.
I have seen two main styles of wear, which pertain most to horizontal SH. First is high & up tight against the pits. The second is slung lower. H&UT is a bit more concealable and not as floppy (when upright or bent over). Lower can be more comfy and less chafe-y. H&UT is harder to put on.
If you lift or are prone to weight gain & loss, a SH will be a grand PITA. Because it will require adjustment with any significant gain or loss. I have not worn SHs for stretches due to this as I cycle through the year and as my workouts trend between cardio and moving iron.
SH are better than strong side belt holsters for driving, but still not terrific or as good as a driving-particular holster.
An ill-adjusted SH may lead to the strap folding back on itself. Attend to poor adjustment PDQ.