Hi grenert, as its is, you can not tell the difference between a US and Mexican made 100, 200 or 300 [ they are modeled after the 275 series]. The technology is the same, its 20+ years old, so they are more than capable of making a duplicate.
They had their faults. If you buy a Mexican 100 and add an external speed control, run through all the speeds; I've exchanged 1 from Walmart that vibrated too much at just one speed 15k rpm, after return I got one that was right, they just didn't balance it right. OTAH, they do balance the motors on the 200 models and up properly which were made for variable speed.
US model had a large fault. In the early 1990s, when Dremel was bought by its parent
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I forget, they quietly added a plastic clutch to the entire model line that breaks under heavy load or age; the motor will lose speed and finally free spin but the shaft will not turn. The part is the 'flex coupler' and is $1 item, but you have to open the Dremel and replace it;most folks can't service it and it led to a large number of service calls and complaints of poor quality; it was actually a 'safety' device. In the late 1990s, they quietly removed it. If you have such an old model just replace the whole $20 rotor assembly with the 100 part replacing the old part. In the USA, Dremel will quietly replace that for free [ you pay S/H] if you complain about the coupler. You can also make your own coupler out of aquarium plastic ~ 1.5cm length clear tubing, I forget the diameter but it must fit very tight, and you can replace it yearly to keep it fresh; the tubing is ~ $1 for 3 feet, regardless, that coupler is not a precise device and it affects the run out of motor's rotation compared to one without it. Other than that, US models suffer less from overheating the speed controller as electronic parts were sourced from Taiwan, Japan and USA, and were better made than the Chinese electronics in the 100 series.
Parts on the 100, 200, and 300 are all interchangeable, including the speed control. Also, if your speed control screws up, you can bypass it completely, and put mains voltage directly onto the stator pins; or buy an off/on switch from Dremel and drop in replace it for the 200 or 300 speed control, or even cannibalize an old unit. The 3000 is a full redesign so the parts are unique, as is with the 4000.
If you're willing to trade short run time and the cost of batteries for convenience, the cordless can serve you well. Early models were NiCD and finicky with charging, and Li Ion chemistry has a calendar life of 4 years, so it will die regardless.
Which model you choose depends on how much torque you wish, and degree of speed control. The 100 series is the most basic and is good for craftswork and electronic repairs/hacks. Its also fairly small and light.
The Chinese copies, mostly from Harbor Freight, can work, but I've seen more of them dead than Dremels. If its not quality control in manufacture, its erratic top speeds [ usually 15-20k, about 10-20k slower than the 100], or easily killed by overheating. It usually will last you a few jobs, just enough for the warranty to expire. The advantage of it is if it dies on you during warranty, Harbor Freight will honor the full replacement warranty.
Saturation, do you think the current model 100 is of equal quality to the older 275 when it was made in the USA? I ended up seeking out an older 395 rather than go with a current model, but I'm not sure there is any wisdom in that. I bought a cordless 8200, made in Mexico I think, and it's worked well for me.