I have herd some good things about them. With the 4x4 units I have herd of people using 1k set upsfor the best light penetration. The hut is 16sqf and that is 800w at 50w per square ft. You could get a nice lumen output with 1k. Heat is always an issue with a 1k because like with any light you want to get with in 18 to 12 in IMO to get the best light penetration.
If you want to go with the 400w I would look at the smaller unit, the hydro hut mini.
Adieu