Agreed, NLS would be the best IME.
Yes, the protein source in NLS is safe long term. It is not just the protein percentage, it is the quality of the ingredients. NLS uses ingredients that the fish can actually digest, so mbunas and Tropheus can thrive on it. Many other foods use ingredients like wheat gluten that artificially increases the protein content. This means that when they test it in a lab they may get 45% protein, but the fish cannot digest all of it, so they may only be able to get 20% protein out of that food. The rest passes through just to breakdown into nitrate (or cause digestive problems on the way out).