I do agree with your moving parts statement but I did buy a 4 inch 13.00 electric grinder from HF going on it's 3rd year and being used hard but I only bought it after using up 2 80 dollar Mikitas - I will admit that I that I most likely got lucky
I bought an angle grinder to clean up a 6 cyl head. wore it out on the first chamber. took it back for a replacement. wore it out by the 3rd chamber. replaced it and finished the job, then took it back and got my money back...
Yeah, its all about luck with that stuff. I bought a harbor freight floor jack over 20 years ago and I'm still using it. It does tend to twist while lifting the car now though. I bought a new one recently to replace it but I haven't gotten rid of the old one yet.