I havent tried the 3Ms....but i have the blaze in 50,60,80....they are somewhat scary...last night I ground the primary bevel on a 1/8" thick neck knife in one single pass....almost too sharp!
I havent been using them long enough to compare to the regular norton ceramics, but ive bee using the same 50 grit and have ground a bunch of blades on it and it doesnt seem to be getting any duller!
A few others here have some, but I havent seen their reviews yet, but when these are gone (may take a LONG time) ill surely be ordering more