I wouldnt bother with no named brands. I think it is better to be safe than sorry. Think about all the time, care and attention you give your fish, then feeding them chit lol.
I once tried buying cheaper food on ebay, but gave up. I used to feed my then tank, 2 blister packs of frozen food a day, 1 pack of frozen bloodworm and 1 pack of lance fish. It was costing me a lot of money, then I started buying the bloodworm from ebay, however the quality was so bad, I ended throwing most away.
I now buy King British flake on ebay, 6kg bucket, and I now buy the bloodworm from my lfs. I just cut back as to how much bloodworm I was feeding, so nowadays I feed mostly flake, and say 4-8 small cubes of bloodworm.
But dont underestimate flake....it is actually full of good stuff for fish.
[for those wondering why I fed so much frozen food, I had at the time 2 large pacu's and two large oscars, and some blue lobsters, they would eat for England!]