The reason I didn't buy from the Factory Outlet is impatience. Otherwise, going by all accounts, I would have had no trouble buying from there.

I wouldn't put the M2 on its side. It was designed to be vertical, just as the 100 and 150 were designed for horizontal dispersion. I've never found the VP150 lacking, so I wouldn't hesitate to recommend it, but I do plan on trying a vertical center (or centers) down the road. If you can accommodate the height of the vertical M2, I'd go that way. Otherwise, I think you'll be served well by the VP150.