I would suggest smaller individuals acclimate better but 1" is tiny (unless captive raised in which case yay). I'd look at 2-3" as they are large enough to take bigger foods and have enough bulk that their metabolism isn't super high.
I've never had an issue getting predators to eat frozen, although my experience is limited to lions, scorpionfish and bettas (worked in a lfs). My trick was to just use live food to begin with, brine for small bettas but river shrimp is good for larger ones. Then when they are responding to food I try dead ones of the same food type and move it with flow. You'd be surprised but it normally works fairly quickly and they begin to take everything shortly after. You can use feeding sticks to wiggle the food in the same way.
Mine hasn't grown super fast but it is partly dictated by the amount of food you feed. If you feed more it will grow quicker but I'm cautious as I believe overfeeding leads to other problems like you see in lionfish. I tend to feed every other day or at least twice a week. I follow the food item total being six times the size of the eye per feeding. Its a rough rule for lionfish but they are fairly similar in my experience and would gorge themselves if they could as well so better to control their intake.
I haven't had an issue with it and tankmates yet. It is maybe 4" at the moment and leaves everything alone. I have it with a indigo dotty, which is similar to your fridmani (well is a hybrid of one) and there is no problems. It also leaves a small orangespot goby alone and even the shrimps (cleaners) don't tempt it. I have hermits and snails and they haven't been predated. In fact the only thing I have seen it eat in worms, both bristle and spionid.
I would say that again feeding is important in controlling their predatory habits. I don't see them as a problem with anything but the tiniest shrimp and fish (like gobies and evoita) tbh. I'm not saying that wouldn't change if it wasn't hungry but I had a tiny 1cm clown jump in the tank from my breeding setup next door and it was hiding under the betta from its parents, who were intent on killing it.
I think you will only find a few reports of them being "naughty" and I would wonder what the actually situation was in such cases, ie did it actually eat something or was it just there when something went missing.
They are nocturnal but tbh I don't really see that too much. Mine is always active in the background and when I approach the tank it is always aware of me and comes out to greet me. I put this down to not having any large fish like tangs to bother it and of course it associates me with food. It also knows that as soon as the pumps go off its feeding time.
I would recommend them to anyone and think a 55 should work. they don't need a huge amount of swimming space but you need to provide plenty of overhangs and caves and because they are predatory and have a protein rich diet, your filtration needs to be good. My tank is the same size but I'm just keeping an eye on it at the moment and have plenty of space elsewhere for it if it does begin to look cramped.
