Is it possible to make them grow faster than they already do?..now as for the topic,I'm not sure if the thiaminase will kill the armatus but some parasite or disease from one wrong feeder might do the deed.If you go the feeder route you'll have to treat every one that you intend to feed to your armatus.
I've never kept Armatus, but I can say from my snakehead experience that snakeheads fed exclusively feeders grew significantly faster than snakeheads fed exclusively pellets (NLS and massivore). I also had similar results with dats, catfish and other piscivores.
Thiaminase will likely shorten the fishes lifespan, however, it's very difficult to say how much. Feeding live fish that don't contain thiaminase would be a better option.
I've lost 2 armatus after I started giving them silverside. So the one I have now, I've gave him feeders till I couldn't get large enough feeders. ( pounding down 6-7 inch feeders and still weren't big enough.) now that he's over a foot I give him tilapia that freshly cut.
Started my armatus with feeders just to get it to eat, then switched exclusively to silversides, loaded with cichlid sticks. As it got got bigger, fed smelt loaded with sticks. As it grew, frozen sardines,yellow croaker,gourami all stuffed w/sticks. During spring/summer, live sunnies. It's 2' now so thiaminase hasn't killed it yet.
Feeding your armatus feeders for life: I'd say good AS LONG AS: the feeders are healthy (but most feeders aren't). I started growing tilapias to feed my payaras btw. And the tilapias are fed lettuce broccoli garlic and other veggies.