I used the loose 2ff in my Knight. Got it right before deer season so I don't know about long term storage. I could get maybe 15-20 shots before cleaning, and the problem may well be plastic from the sabots more than the powder residue. I can tell you with absolute confidence that it's WAY easier to clean than BP and cleaner than pyrodex. One wipe with Windex, one clean dry patch, and you're done.
As for power, the "shoulder" test says that it's close to BP. Didn't chrono it. Shoots maybe tennis ball groups at 100. Good enough for deer. YMMV.
IIRC, I read somewhere that it's different from the American Select. Dunno.