Usually the HF stuff is at least usable. I have never tried one of their bench grinders.
BUT several years ago, I saw this nice looking heavy no name bench grinder at local Chinese tool place for like $10 or maybe it was $15. Said 3/4 hp which I knew was greatly optimistic but base cast iron and sure big enough to have enough motor inside to at least do ok.
Got it home. It started spinning easy enough. Just reshaping end on screw driver bogged it down. Seriously, it was unusable. Still setting on a barrel in back room. I ran across little doityourself article where some guy had disassembled his cheapo Chinese bench grinder, removed the motor windings, etc. and installed a pulley inside on shaft, then cut slot in back of grinder motor housing and ran a belt to a real motor. Said it worked ok. Sort of like people in old days buying a mandrel setup and made a grinder, using a washing machine motor and belt to power it. Even 1/3 hp motor (a real one) should be enough for average use of a 6 inch bench grinder. But real half hp motors not that hard to come buy if you are willing to custom make a perch to use one say off an old pump or something. And I've seen even real 3/4 motors go cheap enough, just want to make sure its single phase and works with 120v AC.
Oh and just curious, I looked on ebay what used REAL commercial quality bench grinders go for. Figure around $200 for quality used one. I cant imagine average home user ever justifying a $200 bench grinder, but hey they are out there if you want one. And if it works well when you get it, for sure it will last lifetime. Also heavy enough that you would have satifaction of knowing any thief suffered greatly carting it off.
Oh here is link to discussion on another forum about chinese bench grinders. http://www.badcaps.net/forum/showthread.php?t=9250
Seems despite their size and weight, the actual motor inside is more akin to one in box fan. Around 1/8 hp at most.