I can only speak about my own experience with one of the refractometers off of ebay... and I will NEVER
use a swing-arm hydrometer again!
I started with a couple of different hydrometers and the readings were always waaaay off from the ones I got from the refractometer they use at the LFS
Before I was gonna buy one of the $110 refractometers they had for sale I decided to try out one off of ebay.
I ended up getting one made in Hong Kong that greatdel always has for auction.
Linky - Hong Kong refractometer auctions
I won it for $20 + $8 shipping and I couldn't be happier.
Everytime I've compared it to the one they use at the LFS
the readings are exactly the same.
I can't see any difference to the $110 one behind the counter.