Adrian, I kept all 3 Mandarines in my 12G nano tank (the first one I later moved to my 120G, and the later two went into the Nano tank at the same time) for more than 1 week to train them eating frozen food. They were doing great in the nano, except they ate so much that I had a hard time to keep the water clean (I hated doing water change all the time). After I put mine in the big tank, I stopped feeding him frozen food because it is hard to keep other faster fish away from the food and he seems to be getting enough pods from the tank anyway.
There is no guarantee that every Mandarine can be trained to eat frozen food, but I was able to train all 3 to eat frozen food within 3 days of time. So if you or your friends have a backup tank with enough pods, and you do not mind going through the trouble manually feeding it everyday, go for it. IMO they are one of the most beautiful fish I have seen.