The cannon is powerful. And it produces true UV light vs LED UV. I agree that tubes are pointless for that much area. The UV Wash isn't a bad fixture. It just isn't as powerful as the UV Cannon is. Also, the lamps for UV Washes aren't cheap either, listing for $49.95 a piece. So price of a UV Wash lamp is the same as a UV Cannon lamp. For the price of one UV Cannon, you can almost get 3 UV Washes however. So the quick down and dirty:
1. Replacement lamps cost the same for both, however more fixtures means more lamps to replace. Point UV Cannon
2. More fixtures gives better flexibility. Point UV Wash
3. UV Cannon is more UV power then 2.5 UV Washes, so UV Cannon has better bang for buck on the power front. Point UV Cannon
4. With more fixtures however, you can cover a larger area. Point UV Wash
Those are the major points I can think of and it works to be about the same. get whichever will suit you better. Do you want one, powerful light with not as much flexibility and coverage but less gear and maintenance cost or several less powerful fixtures with more flexibility and coverage but more upkeep and gear to lug around? Personally, I would go for the washes. I like flexibility and need it in my work. Extra gear and maintenance cost means nothing since I have guys lugging it and clients who pay for it.
Also, one note. When buying UV Wash/es, check the lamp before you leave the store/as soon as you get it in. They have a tendency to break in transit.