I try all my fish food, but only when I first open the package. The fresher the better. I have not tried FD tubifex because the package had been open for several months. I've had live shrimp I netted in an estuary (may post that on youtube sometime). I figure, if it's good enough for my fish, it should be good enough for me. (I like to treat my fish well.) I've been treating some fish with frozen pollack fillets bc they're cheap... ironically, pollack is the type of fish most frequently served at Notre Dame's dining hall. The inside joke between my roommate and myself being: "What's for dinner?" "Fish food."
I'll try anything, not too keen on the frozen stuff as I can't tell how fresh it is. Bloodworms probably don't taste too good, and would be worse with freezer burn. I may pick a few mysis shrimp off the pack in our freezer later though..