Unique is certainly very versatile. It is useful for full-powered loads for many semi-auto pistol and black powder era revolver rounds, standard power 12, 16, 20, and 28 gauge shotgun loads, and lead bullet rounds in centerfire rifle rounds. It's not just subsonic rounds, for example, you can use Unique to shoot a 160 grain lead bullet from a .30-06 at about 2000 fps.
Unique is notably dirtier than many other powders, and is by far most notable in shooting revolvers as the soot exits through the cylinder gap and gets all over the frame, cylinder, and the shooter's hands. Shotguns have a little more fouling in the barrel than with cleaner powders (much easier to clean than with a revolver), and in high-pressure rifles it burns clean as a whistle as those pressure levels are more than enough to completely burn that powder.
Typically issues with case fill involve using fast-burning dense powders in low-pressure cartridges, most infamously Bullseye in the .38 Special. If there is a very small charge volume in the bottom of a large case, it is not too hard to accidentally miss a double charge and blow up a gun which is only rated for low-pressure loads. Unique (or Universal, or any other medium burn rate medium-sized flake powder) is bulky enough that it would be obvious if you double-charged a case. Many powders suitable for handguns, with the notable exception of H110/W296, are quite insensitive to case fill.