Well, I carried in shoulder rigs on the job for years. One job included executive protection which meant moving dignitaries from place to place, same as Secret Service and worked with them on many missions when a pres or vp would move through our area in the US or wherever. The biggest risk is during movement, was getting the gun out while in a car was a big issue. I do not ever recall it being an issue for me, because close to 100% of the time, I had a long gun. We were authorized sub-machine guns, short shotguns and car 15s. So, it was as much for comfort as anything else. In those years I carried both revolvers and a 1911. Now when walking away from the car it was a great method of carry.
I have 3 of the Miami Classic, made famous by Don Johnson in the series Miami Vice. My early ones were actually labelled Jackass Leather Company. The later ones, say Galco. I have them for the 1911, J frame, K frame and N frame, the holster just changes with the gun with the rest of the rig staying as is. The revolvers have small bullet pouches that holds 6 rounds of ammo each, the semi rig has a pouch that holds 2, 1911 mags. On the off or left side, mine also had a handcuff case. So the weight of the ammo and cuffs would help offset the weight of the gun on the other side. They are pricey and originals like mine are collectors items and even more pricey. I have instructed my wife to dress me in one with a handgun for burial. Not sure if they will do that. There are copies out there and the technology is pretty simple so an aftermarket should work fine. One caution, the ones made out of nylon suck, they are flimsy and do not stay in place like leather. The rough side of the leather will be against your shirt and keep it pretty much in place. We often had to run from place to place as soon as the car driving the protectee slows and you do not want any more bounce than necessary.
I also sometimes used an upside down holster for a J frame. It was elastic and held the gun well. I also used it for years for CCW. It is a very fast way to get a gun out, sitting standing, kneeling or perhaps sitting on the pot. Went to potty once on a camping trip and a snake got to close while I was in that award position. You did ask if people had experience. Not aware of anybody that makes one now.
Third, I use a Safariland holster for big bore carry. The one I have is made for a 6 inch model 29 SW 44. It carries my 4 inch well and it carries high capacity 9mms well and carries a 1911 well. It is a vertical holster with a cross snap and you cannot lose a gun while on a horse or 4 wheeler.
I seldom carry open except while in the boonies or hunting but just do not see much reason to ever let the public know I am carrying. If somebody needs to know, the big flash and noise should be their first clue. But then I am old and slow and just do not want to be in a fair fight, way too much risk. FWIW
1. Jackass, now Galco. 2. ammo pouch and cuff attachment. 3. Safariland with SW Govenor. 4. J frame holster with Model 60 in it and other is the model 637 with crimson trace.