The tetragonpterus are great dithers, had 5 but lost 2 so am down to 3. I bought the smaller size(2-2.5inch) and they easily put on I'd say anywhere from .75 inch to 1 inch in a month. Don't know if the growth will continue like that but I was happy to see them put on such size because they where small when I got them. They're aggressive eaters and semi aggressive among each other but ignore everyone else. They don't damage each other but do this weird thing where they seem to take turns chasing each other with none showing a clear dominance. The chaser and chasee seem to change roles the minute the end of the tank is reached. A bit on the bolty side but they're still fun to watch as they tend to run away easily from your approach but run just as quickly back once they realize it's you and your their source of food. They haven't eaten from the surface for me so I've been feeding them 1mm sinking pellets and they also eat shrimp they manage to snatch away from the pike and papyrocanus afer. They eat like Piranha or bucktooth tetra swooping in snatching grabbing it's chaotic but very cool to watch. The other thing that makes them great dithers is they really move non stop. Silver Dollars will chill often with one another and many fish will kind of hover or slowly cruise but these guys are non stop movers bolting here and there so far. They add a lot of high energy activity to the tank.
I never tried freeze dried since I feed my Trachy's, Apu and some other fish shrimp so when preparing to feed the others I just made some for the Tapajos. I started stuffing the shrimp slivers with pellets but it's tedious because of the size of the strips and pellets. I eventually just started rolling the shrimp in 1mm pellets they sticked well enough that the pike consumed the vast majority and anything that fell of was picked up by the other tankmates. I think that's what actually helped get mine onto pellets. The pike got used to the feeling of the pellets in it's mouth. Between that and watching his tankmates eventually he started eating pellets on his own so now I feed 4mm pellets to the pike straight. I love the fact that the Tapajos is usually out and about and if he does disappear among the deco my approach always brings him running to the front. Those are some nice colorful tankmates you've got with yours. Since mine has been alright I think yours will get along fine with your choice in tankmates. I also have to say I find it amazing that my pike only shows aggression only to the other cichlids, he shows no interest at all in the Tetragonopterus or Afer.
Good luck with your man, can't wait to see who gets the faster growth out of them.