Ok, I'll take exception to Felix's statement, if only to shake the boat a bit.
I doubt anyone can rely on the quality of the chemistry of high dollar drugs any more or less than others for one reason... there would be more profit in counterfeiting an expensive name brand than a generic inexpensive one.
Of course I'll agree, a larger volume purchase is best for consistent loads, once you have found the powder that performs best for your application. Then all you need be concerned with is perhaps freezing temperature in winter, and 110% in summer with no shade.
Large difference in performance for bottleneck cases near max!
If it wasn't for the challenge, handloading would just be for cheapskates!
And I am certainly one of them.