I've had one of these little guys for over a year now and its still as shy (won't feed if it can see you) but will take anything you put in the tank, flake, pellets, frozen...........
The only problem I have had and the reason it lives alone is that it killed a leopard puffer. I say killed as I witnessed the puffer swim near it and then saw the scorp repeatedly stab the puffer with its dorsal spines. I'm not sure if this is an isolated problem or if something else was involved (the puffer seemed in really good health) but it put me off mixing it with anything else.