I don't have much experience of Derbys apart from the odd giveaway packet I've had, but I bought 100 of the Premiums in a spirit of optimistic adventure.
They're better than the other Derbys, but, as others have found, they don't seem to be very sharp or stay the course for more than a day or two. Not exactly top of my "go to" list, I'm afraid, but I will admit I haven't tried them in many different razors. They might perhaps be useful in taming somewhat the House Bacon Slicer aka Ikon Tech.