I have taken most of their courses. Start with ECQC...it is the most fundamental and the least likely to result in serious injury. Attrition rates seem to run around 10-15% every time I've done it and I've seen people reduced to tears in it. You don't want to start with one of the brutal ones. ECQC is still a real ego-crusher. You will get ####ed up.
I think the 1911s I've taken have been a Baer UTC I tuned a bit, an old Colt that I tuned, and a Norinco that I built which had extensive alterations to the frame and slide. Mostly grinding...I didn't have to weld the rails on that one.
Never had an issue with any 1911 I've checked over. But I do build 1911s.
What is probably more worth asking is "why should users be fixated on guns that shoot when muddy?" Mud is not really a big problem for many handguns. They're pretty much closed systems other than the barrel, and any handgun that gets its barrel clogged with mud will get wrecked if shot in that condition.
If you take a well-built gun and shoot it, about the only thing that will shut it down is lack of maintenance, or enough dust to cake in the action.
So if you really want to hunt down guns that allow you to get them really dusty while you don't bother to lube them, that's up to you...but that strikes me as a real waste of time. If you can't lube a handgun once every thousand rounds or two...I don't think handguns are the tools you need to solve your problem.