the big one pictured above is M Dayi. imo they are very similar to armatus. i wouldn't be surprized if they are a color varient ect or subspecies. not sure if the classification is made purly on collection/distribution or gentically with these guys.
I sold my big armatus awhile ago.. and the tiny one i got ended up jumping out( the same day another fish from the tank above did as well, was very odd.). I have not seen much differences besides coloration. the growth rate has been pretty close, as well as temperment, feeding preferences ect.
And i did end up moveing the fire into his own tank for the time being, my other m dayi despite haveing plenty of room harassed and chased the lil guy relentlessly. Ive found after an initial hour or so if the aggression continues it will escelate to death either from stress, or jumping. hes doing fine now, 20 gallons to himself and all the live blackworms he could want.