For me Unique is good for 20ga,28ga,38,357,44spec,44mag,45colt and 45acp and when I had a 9mm I used it there also.
Most of my shooting is killing paper with light to maybe mid range loads. If I want to step up the 357 and 44mag for something larger I have 296 on hand for that purpose.
I have a load for the 45 colt with Unique that is suitable for deer and this year I will have one for the 44 special also,probably 7.5 grains under a Keith swc.
Many years ago $$ for components was a bit thin,so I started using cast bullets. Also back then there were not as many powders available as there is now. So to me it seemed cheaper(more frugal) to find one powder that could do most of it for me.
By using Unique I keep my inventory of powder to just a few and I buy it in 8lb cans. Yes in light loads with cast bullets it is a bit sooty,dirty,smokey. But I have to clean the handgun anyway.