5% variation on frequency will put it 57-63 Hz. That's a little loose for some items.
It's fine for motor related stuff (A/C, Fridge, etc..) but will show up on the screen of a TV when other stuff kicks on and off..
Is it junk? Dunno. I would expect an air cooled diesel to be pretty darn loud. I may be wrong though.
Go try one out and let us know.