I used Derby Premium blades exclusively for FFFMM. After a month of using them solidly my jury is very much out. I found that they were highly variable and had shaves using them that varied from BBS to terrible. A good blade was very sharp and satisfyingly smooth - a bad one seemed to start out dull. So when they're good, they're great - but are awful when bad. YMMV but for me I can't rely on them, and that matters.