Thes weight capacity of the Ultimate brand stand is over rated, a twin reverb will break it in time. OTOH, I've found it seems to hold up fine to single 12's and smaller cabs and the occasional use with my 50 lb Acme B2. I use it on big stages to turn a cab into a monitor.Marc - on the page you linked to, all of the reviews mention that that particular stand has a design flaw which casues it to break pretty quickly. Have you found this to be an issue with yours?
At cafe size gigs I usually borrow a chair or a bar stool. However, if you must be prepared, you might try sitting the little Wizzy on a music stand. I had to use one in an emergency situation and I found it worked OK with my 20 lb Ampeg PB110h as long as the weight was centered over the shaft. If it works for you, cut the tray down to size with a hacksaw or skilsaw and cover it with velcro.
Joe