I think they're awesome for their intended purpose - to rinse the carpet. The SD will pump more water through the carpet and successfully recover it - than any other extraction system (including truckmounts). So when it comes to rinsing, the SD is the king.
Where it falls short is in the area of heat - you're cleaning with cold water. It also lacks pressure, since you're only getting about 30 psi from the city water supply. But these two shortcomings can be addressed by pre-scrubbing. If you'lll intensify the "A" in the cleaning pie (Agitation), and then give the carpet a good rinse with the SD - you can get great results.
When you add to the fact that the SD also has auto-fill and auto-dump built right in, the SD's becomes a pretty slick machine. The only limitation on the auto-fill and auto-dump is that the hoses are limited to about 200 feet. However there is an optional additional pump that can be added so that you can run longer hose runs. One further downside is that the hoses can be kind of a pain to work with, but they're manageable.
I think the Steamin Demon fills a very important niche in the commercial arsenal. That's why we sell them...
http://www.excellent-supply.com/Steamin-...p_266.html
All in all I think it makes a lot of sense for commercial work. A god encap program negates the need of relying heavily on HWE. However when the need arises, the SD can cover a lot of ground with its unsurpassed level of flushing water through the carpet.
Another convenient alternative is our new TruckPort portable. Plenty of power in a convenient package. It's a perfect balance for efficient hot water extraction. It doesn't have the unsurpassed water flow that the SD has, however it has high pressure water 0-500 psi, it has 2000 watt heat, and it has tremendous waterlift at 225". Plus there's an auto-fill and auto-dump option if you want to add it.
http://www.excellent-supply.com/Steamin-...p_266.html
Either of these two machine options makes a lot of sense for a commercial cleaner to handle the periodic need for extraction cleaning. Hope this gives you some food for thought.