My Uniflow does fine with Unique, and I use the large cavity drum (I think I lost the other one, if I ever had it. Never used it.
If you think Unique doesn't meter well, go use an IMR stick powder, then tell me its not better than that.
Not as good as fine ball powder that measure like water, but I never had a problem, or heard of one before the Internet.
I have used Unique in smaller caliber cases but its not optimum even in .357. In .45 caliber, its great for me. 6.5gr 230gr .45 ACP is ball ammo duplicate, 8gr under a 250 for .45 Colt in a Colt, 10gr in my Ruger Blackhawk.
Been using Unique since the early 70s, see no reason to switch to any of the newer powders, as long as I can get Unique.
Best for "full power" medium to medium heavy loads, not at its best in light loads, and not suitable for the very heaviest loads, it performs well, for me. you may not like it, but that doesn't change my mind.