Just setup a hydra 26hd a few days ago. I've been out of town the last few days, so I have little feedback. Setup was easy and corals seemed to respond immediately by showing a slight change in color in corals that had none after just the first day.
I'll be home tomorrow night, so I'll have more to say after not seeing the tank for 4 days.
Btw-I'm running an sps dominated tank. 17g (24x12x14)
I am two weeks in on a Hydra 26 HD. The Hydra 26 is lacking in integrated wireless and Hyperdrive. Its worth spending the few extra $ to get the HD version. Also the color LED blend has been optimized.
Growth to early to tell, zero issues, yes it will work over your size cube.
I have written reviews on it so a search will yield the answers your looking for.