I've also used a variety of Kens products for years and had good results. He sells lots of foods of his own and lots of the commercial brands.
What fish will eat and what is nutritious are two different things. You really need to look at the ingredients - they're all not the same.
One thing I learned from Les Wilson's talk on fish food (at the ACA) and hopefully in 2015 for our club is that spirulina is bitter and unpalatable for most fish. It needs to be balanced with other ingredients or the fish won't eat it. That said, I've fed Ken's Tropheus Lovers flake with great results (as well as used the pure spirulina powder).
I'm a big fan of his new medicated flake. There's a ton of garlic in it and the fish eat it up (a spoon full of sugar helps the medicine go down)
Matt