It has it's loyalists. I'm not a fan-- I used it for a while years ago; reluctantly, because I moved from Florida to a new area and couldn't locally find the foods I liked. Was never impressed with using Hikari. At one point I'd gotten some really beautiful C. mloto and noticed after a few months they looked dull. I also had a frontosa that wouldn't eat it. I suspected food and this started me off doing several years of pretty thorough food testing, which in my area meant buying food online back then. Also spent a lot of time reading and learning about nutrition and ingredients. Hikari wasn't impressive. Okay, so that's anecdotal, personal opinion, without a lot of detail or hard data. There are a lot of opinions about fish food.
Here's the other thing it comes down to for me. Compare the first several ingredients listed, found these based on a quick search for ingredients lists--
Hikari Cichlid Gold: Fish meal, wheat flour, flaked corn, brewers dried yeast, corn gluten meal, wheat starch, rice bran
NLS Cichlid formula: Whole Antarctic Krill, Squid, Whole Wheat Flour, Ulva Seaweed, Chlorella Algae, Beta Carotene, Spirulina, Kelp, Garlic
Most fish fish foods use some form of wheat, often as a binder, so the difference there is amount, Hikari lists it twice indicating higher total content. Another difference is corn products, brewers dried yeast (a beer brewing by-product), and rice vs seaweed, algae, spirulina. Very different approach, aquatic products in NLS vs. cheaper agricultural products in HIkari.
You be the judge on ingredients, I saw the difference in my fish. I don't have any special loyalty to NLS, I used to also use Omega One with good results and I'll tell you that during over 15 years of using and comparing the two brands, some species looked better on one, some on the other. With most species I didn't see much difference (also, some Omega One products were better than others and, to be honest, I see a difference in some fish between different NLS products). I stopped using Omega One when they went to cheaper formulas on their products I liked. Some years ago there was also another food on my list that I can't think of at the moment, which I rated a little lower but acceptable.
So that's my review. While food questions always bring out contrary opinions, Hikari is low on my personal list, based on experience and ingredients. I also agree with Hendre, good water is just as important to bring out the best in fish.