Unique is easy to ignite, but it is a low(er) pressure powder meaning it doesn't generate a lot of pressure for it's weight compared to faster powders like Red Dot, Clays, Titewad. That is a good thing because it means you can push a bullet faster with Unique without going over pressure compared to those faster powders.
The down side is that it needs to run in the mid to high pressure range (> 10,000 psi) to burn cleanly and closer to the 20 k's to burn completely in a handgun length barrel. The unburned flakes are not really a problem. OTOH, if your cases are sooty, if you get blowback in your face, then you are running too low and the case is not expanding enough to seal off the gases.
Hodgdon's Universal is a competitor to Unique and tends to burn more completely even in underpressure instances, but will still be sooty/smokey if the pressures are too low and it's more expensive.
When I first started with Unique I was over-conservative and was loading low charges in 45 ACP which is a low pressure round to begin with. I was getting blowback into my face and after a shooting session, I swept up a pile of flakes in front of the shooting bench that seemed like it could load up several more cartridges
I like Unique. I don't have problems with metering that some other loaders have. I just make sure it is loaded to where it burns clean(er). I use it in 9/38/357/40/45/.308(light charges). In fact I picked up another 8# jug last November before the craziness and am very glad I did.