Like many on here, they were the first blade I used.
At the time, I thought they were fantastic. They were so much better than any blade I had ever used before (i.e. Mach 3, Fusion etc). But then I tried a Gillette Super Thin. I then realised that Derby's are rubbish blades.
However, I still like them. I like them because they were the first DE blade that I used. They were safe and quite mild, which allowed me to ease into DE shaving and improve my technique without too much fear. If I had dived straight in with a Gillette Super Thin or a Feather (both much better quality blades), then I may have cut my face to ribbons every day for a week, then given up and got the Fusion out again.
So they are rubbish blades, and I would not use one again. But I like them because they allowed me to get into DE shaving in the first place.