I've just got a refracto too, been reading up quite a bit.
What I understand is that the refracto is pretty much bang on for everything before fermentation has started, however once there is alcohol in the mix you start to rely on some quite complex formulae, including some fairly intricate correction factors for your own equipment, which you can't really calculate without a highly accurate hydrometer.
So unless you own a good narrow-range hydro and calibrate your correction factors precisely, your refracto will be quite inaccurate in predicting alcohol and backtracking to OG will probably be way off.
Personally I'd rather use a hydro once everything has cooled, but the refracto will be a huge timesaver on brewday.
I haven't brewed with it yet, so this is all theory based on many hours searching the net and reading old HBD and Promash discussions...
YMMV etc.
[post="55626"][/post]