My personal thoughts about gel food are the same as they have always been, and while I have admitted in the past that gel foods can have their applications under certain circumstances, I would not use them to feed my fish.
Having said that I have no issue with feeding fish aquatic based plant matter as part of their diet, even a main part if the fish is classified as leaning towards that type of diet in the wild. All of the original NLS formulas contain aquatic plant matter, and always have. Not just kelp, but also seaweed, micro algae, and spirulina. And not just a tiny amount when you add it all up, it's a good portion of the formula, which was one of the main reasons I first began trialing NLS many years ago.
Now New Life has taken it a step further, and came up with a formula (AlgaeMax) that is based on 9 different sp of aquatic plant matter, along with krill for additional amino acids and fatty acids. Would I feed that exclusively to my herbivores, probably not, but I would use it as a portion of the diet of a fish classified as a strict herbivore if it was available to me. Not because I think that it would make a big difference either way, but it couldn't hurt, and over the long haul it might be slightly better suited to the fish. Hard to say without running some long term feed trials and testing for digestibility, growth, overall health, etc.
I've seen a LOT of foods over the years that stated they were based on plant matter (some were/are, some not so much) or the plant matter was more terrestrial based, and not aquatic based. Or they were based on a single plant, such as kelp. What New Life has come up with is actually pretty unique, and I'm sure they will do well with it.
