Hall is 16 x 10 metres, and I'm considering getting four of these. I also considered some Showtec UV LED Bar 120cm, but the seller told me their beam angle is rather small so lighting a hall might not be successful.
Regarding the old school 400W UV cannons, I actually own two of them. One issue is they're big, and I don't have much car/van space. But the other issue is, at the times I've tried to use them, I was really not impressed with their output. It may have been to do with the light level in the hall, or the angle, or whatever, but last time I tried them they didn't seem to be contributing much. I mainly wanted some UV reactive tape on the floor to glow, and that just didn't happen.