Flood and drain is great and some plants like it best, however, constant flood can work too and as long as there is enough flow and aeration it works fine as long as the surface of the media stays dry.
There have been trials run over at BYAP where they are running three systems.
Siphon flood and drain
Timed flood and drain
All three systems seem to work well.
The Constant Flood might be a good way to go while cycling up and whenever there are water quality spikes.
Or if you have to add more grow beds but don't have the fish tank or sump tank capacity to handle more water level fluctuations you might add constant flood beds.