I under stand the the gas buster is designed to keep gas, particularly on SBR or supressed, weapons from hitting you in the face.  

My question is whether the unit vents gas out to the right side of the handle, where a left handed shooter's face would be?  

Yes it does.

Some say it does.  I didn't know how it was designed when I bought it but it's never bothered me.  Better than stock IMO.  I'm a Soutchpaw in case you haven't figured it out already.

Try before you buy.  I shoot with my head fairly far back on the stock so that may have something to do with it.

Another southpaw here.  I shoot nose to charging handleand even though the PRI Gas Buster is designed to exhaust gases to the right side, its a lot better than the stock CH.

This is a simple test:  generously lube your BCG with CLP just before a shooting session and shoot a few rounds with both CH's.  You will easily notice the difference in CLP drops sprayed pass the CH in your eye portection glasses with each CH.