I don't think they were dishonest at all. The light DOES cover a 3'x3'. I just doubt you'll get a good yield from using only 1 of them with no other light. Based on the growth I had at 3 weeks of 12/12, I predict that a skilled grower could pull about 5-6 ounces per harvest from a single XGS-190 over a 3'x3' canopy.
Obviously, we'll start to see more results as other XGS owners catch up to where I am with their grows. And once again, don't take what I say as hard science by any means. Everything I've said is based on my own brief experience as an XGS owner.