I brew AG, add Buffer 5.2 to all batches, Campden / Water filter for chlorine & batch sparge.
I'd be wary about the Buffer 5.2. The one thing that is known for certain is that there is some blend of monobasic and dibasic sodium phosphate that make up some portion of 5.2:http://www.homebrewersassociation.org/forum/index.php?topic=1125.0
Which means you're going to be adding a hell of a lot of Sodium to every beer at the recommended dose of 5.2.
Also, if the only constituents of 5.2 are the phosphate salts (which seems like a safe assumption when you read phrases like, "5.2 is a proprietary blend of food-grade phosphate buffers" on Five Star's website) then 5.2 would not be a very effective buffer.
Monobasic sodium phosphate has a pKa of 7.2. In general a substance's buffer capacity is maximized at that substance's pKa. At a substance's pKa ±1 the buffering capacity of that substance is 33% less effective than at a substance's pKa. So monobasic sodium phosphate has a pKa of 7.2 and its effective buffer region is 6.2 to 8.2. According to Wikipedia (which is a great site that is highly accurate all the time and always will be forever) a blend of monobasic and dibasic sodium phosphate has a buffer region of 6-7.5 (http://en.wikipedia.org/wiki/PH_buffer#Useful_buffer_mixtures
) I don't think it's unreasonable to say that a buffer composed primarily of "food grade phosphate buffers" would be a buffer that would not be effective at a pH of 5.2. Chemistry 101 does not support Five Star's claims.
HOWEVER, if 5.2 is a buffer solution that is made with phosphates as a constituent with other buffers then it may work, although, anecdotally, I've yet to hear a scenario where someone with a reliable means of checking pH (a calibrated meter) has said that it works in both a Stout and a Pale ale. I'd be surprised to hear from that person.