I've gone through over 24lbs of Sta-Ball since it came out. IMHO it has far more "pros" than "cons".
At first, I bought it because that's all I could find (especially in any quantity beyond just 1lb or 2). Then, I kept using it because it meters so freaking easily and I didn't yet own a precise powder dispenser... One can drop StaBall straight into cases out of a cheap volumetric powder dropper, and if they develop good technique, achieve performance/consistency as good or better than the Chargemaster crowd, even approaching the performance/consistency that Autotricker owners are used to.
Just dropped straight into cases: if one goes slow, powder for 100rds takes 10 minutes, and it'll yield stuff that's fine for practice out to 1000 yards. This can also be a "con" sometimes because many guys won't bother trying to load charges to +/-0.02gn like they would with extruded stick stuff. (This is a mistake IMO because dropping a bulk charge and then trickling up with it is a piece of cake and nothing like the sheer torture of manually trickling stick powders.)
Thing is, in my experience, it doesn't do one any favors as far as ES/SD numbers are concerned, and makes one work harder... guys who are used to H4350 (forgiving) or Varget (the most forgiving IMO) will need to work harder to see numbers in the same ballpark they're used to. In a way, it made me a better reloader, as it forced me to clean up my process to see consistent single-digit SD numbers (which now makes working with shit like Varget child's play to get stupid low SD's).
One huge "pro" it has (besides just being available) is that being a ball powder, case-fill isn't nearly as important as with stick powders. One can use it to slow down their loads to a speed they like if they want to (to not cook their barrel as fast, lower recoil, etc), and even when the rounds start to sound like salt shakers it still shoots fine.
Supposedly, Hodgdon has more "temperature-stable ball powders" coming out in the same type of vein as StaBall, maybe better, could be cool...