Reductio ad absurdum aside, not many folks have said they're awful. Or even bad. Most of us have just pointed out that they have issues that have to be kept in mind, and that many ranges and range officers stop just short of immitating the robot from the original Lost In Space, making training with them problematic.
I own one. I've used it. It's not AS comfortable to me as IWB strong side hip (probably mostly due to being used to belts and not suspenders, which the tie downs can mimic), but if something happened and I couldn't wear that way for a while, I'd switch to the shoulder holster. I'd also make sure I kept those issues in mind. It is not possible to follow rule #1 with a shoulder holster, though to be completely literal it's probably not really possible to carry and follow Rule #1 100% of the time even with strong side hip.
Safeties and other mechanical parts break. I don't worry about it, but I keep that in mind whether I point the thing at my thigh and foot, or the guy behind me.