I got one of the early sharpeners (so 20 years ago? sort of a biscuit cutter shape) and was not impressed. This last blade I replaced was just dull, no knicks, and I thought about digging the sharpener out of the drawer and trying it, but then since I already had the replacements on hand I just wasn't going to bother.
I keep blue tape in my sewing kit, one of the times I use it is to seal the used blades. Right now I have a spare case clearly marked as used.