Yep...it's rightly been called, "Flaming Dirt" over the years. But, I've used it for some very successful loads irregardless. The newer versions of Unique...say in the past 10 yrs or so, are better, but still 'dirty'. I've got top performing loads using it in: .380, .32-20, .32 H&R, .38 Spl, .38 S&W, .357, .40 S&W, .41 Magnum & Spl, .44 Spl & Magnum, .45 ACP, and lastly, it is THE POWDER for .45 Colt. As a powder, it's versatility is hard to match with any other available, and has been for over 100 years.
My primary objection to using it is its miserable metering consistency through my powder measures: RCBS Uniflow with the "pistol", smaller sized cylinder; & my Dillon 550B's proprietary measure. With Unique, I see +-0.2 grains over a 20 case sample. And believe me, I've used every technique available as well as some minor modifications to my measures, in the 50+ years I've spent with this powder. Truth be told, at least with .38 Special and bigger cartridges, that amount of drop variance does't affect group size out to 50 yds at least. Face it, we're not talking "F" class long range rifle competition here.
All of that notwithstanding, Unique's a good/great powder and is truly "unique" in its broad applications. While it's cleaner burning nearer the top end of available loads in my experience, we all know, we clean our guns after every use, so its black soot residue should not be a deal-breaker. Too, I don't shoot a cpl hundred rounds of it through my guns at a single range session, nor do I participate in any of the handgun games currently in vogue.
YMMv, Rod