During veg it is very fast, Stalky, healthy growth. Like nothing I have personally experienced even with Metal Halide.
For veg I would look at the 100W models personally. I'm using two in a 3x4 with beautiful results. 4 over a 4x4 would be turbo veg!
On the 420/pontoon, I would now honestly say 1 as a sole source for best quality will cover a 3x4. My total yields have seemed to be limited to the wattage. Same light bigger area, yield stayed the same.
The pontoon has it's own power cord. When plugged in (timer on) the 660's come on. When you unplug it, the 660's go off and a few seconds later the 730's come on for 5 minutes or so powered by a battery that is recharged during lights on. The pontoon is a trick piece of equipment. That is why I struggle to move away from them.
I think 2 of them in my 5x5 would do what I am looking for at 920W
I do think the pontoon led combo is putting plants into flower sooner/consistent. Look at my cup girl