My P. saulosi love Omega One Veggie Rounds. It has fish meal in it but spirulina and kelp are the first listed ingredients. I break them up and distribute the pieces among the dominant males' "territories." Putting just one wafer in starts a fight.
Ken's Veggie Flake is pretty much all veggie, I believe. I have tried it and they ate it but not with the same enthusiasm as the Omega One. It is relatively inexpensive.
Mine do like zucchini. Not much luck with Romaine lettuce. They eat Java moss like spaghetti.
I have not tried the others.
I feed my Mbuna their veggies first, and then put in some meaty food for other species in the tank, which will not touch the veggie food. The Mbuna will eat it, but I figure that they at least got their roughage.