a) If I'm reading this correctly, you got 100 blades for $5.65? That's $0.056 per blade... yeah you did alright!! More than alright...
b) IMO Derby blades are great. Very smooth, very mild, you actually would have to try to cut yourself with one of these. Some guys don't like them though for being too mild. I guess you're just going to have to try them and see for yourself. :)