Yes, the Miller home office is in Appleton, Wi
It has about a million sq ft of manufacturing.
There are also a number of manufacturing business units surrounding the Appleton area. The TIG products are in a town called Greenville, next to Appleton and that is where the Dynasty products are made.
Miller has its own circuit card design and assembly area at the main facility in Appleton.
The foot controls are also made in Appleton and they do use a clogged belt/gear driven potentiometer. And as you stated, it is a simple design and yes it is reliable.
Out of the 800 Motorsports machines I'm responsible for, foot pedals are the least of my concerns. I can say I've never had one just "jump" a cog or fall off!!?? If you've ever taken one apart, you'd see it's about impossible to fall off since its under spring tension and the clogged gear has a shoulder on it.
My biggest problem with foot pedals is people dropping crap on the cables and cutting the wires.
I have seen some potentiometers wear out over a long time of heavy use but those are easy to replace. You'll have that with any type potentiometer from any manufacturer.
Another design feature unique to the Dynasty 200 is the inverter engine.
Our engine is a universal design that works on any input power variation from 100V to 600V single or 3 phase. Other manufacturer's only work in certain voltage ranges like 120 V or 230V but not anywhere in between. So if you are using a 230 V input, if the power drops below 200, or whatever their "tolerance" is, your out of luck.
The Dynasty will run on anything.
I've even ran it on a generator that was running out of gas and the engine was hunting all over the place.
You also asked about transformers...
Since this is an inverter, there are no typical transformers. This is an electronic power conversion process. The transformers are extremely small and built with a special Litz wire. They don't fail.
Miller does make it's own transformers for welders AND rotors/staters for engine driven products.
Hope this helps you decide.
Ultimately, I hope you get to try one. You know what opinions are like