Yes, they are, but they are a fabulous "gate way" food! Feeding my female blood worms got her to eat pellets.
You might want to try to get some freeze-dried ones (like a couple bucks at PetCo the "betta" kind) and feed those for 1-2 days, completely fast for one day, then try a new brand of pellets. It worked for me!
My feeding is normally pellets. My male is a pig and eats a bunch, which I'm cutting him down on, and my female eats about 4 pellets a day. Each day they get a small piece of bloodworm, and they get the fruit flies every couple of days. Especially when the breeding in their container gets out of control.... o.O
None of my nine fish will even pay attention to a flake. :S I do try to feed them with it once in a while, but not too often. I think of flakes as the 'vegetable' of betta food. No one wants to sit down and eat a plate of steamed broccoli for dinner, right? hahahaha
I know, it's horrible, but oh well. Like I said, I try to give it to them once in a while. Most of the time, my bettas get pellets (good brand) and freeze dried blood worms.
If I can find the right brand, I buy frozen BABY brine shrimp. Let a little cube unfreeze, and give them a few drops, and the LOVE those!!!
Just keep it mixed up. That's the best thing I think.
Also, I pick two days, (never the same two days) and skip feeding them those days. It helps keep them from bloating. But if they do bloat, boil a pea, peel the shell off, and give them half of it. When I do this, I ALWAYS give them half a pea, the next day, they go into a QT tank, for 24 hours with nothing to eat after, then back into a CLEAN bowl. :) And they are hap hap happy little ones :)
But if they won't eat a pea, mush it, and dip their favorite food in it.
Definitely mix it up! My bettas never know what they're getting. One morning it is pellets & blood worms, the next pellets. Sometimes for lunch they get pellets, or they get fruit flies. They always are waiting at the top to see what they get! Hehe :3
My mollies & GloFish as well as snail loved those.
I haven't tried them on my betta's tanks, though. I feed them regularly enough. Those blocks dissolve into the water if not eaten, and they do raise the ammonia. I wouldn't suggest it unless you are putting it in for a day, then removing it and tossing it out. They're good for 5 gallons + though to leave in a couple days with water changes.