I've used them. You get what you pay for. It's probably not going to give you as good an end product as if you paid $100+ for a kit... However, if you typically drink $5-$7/bottle wine from the supermarket like Barefoot or the other bargain brands, you'll probably be happy enough with the results.
Like madmike said, you can use more than one can per batch for a stronger flavor. I've been happy enough with one 46oz can for a 5 gallon batch, but the instructions on the can actually suggest using two.
Like turner said, you'll need to get your acid and also yeast nutrient and tannins and of course yeast, since none of this stuff comes in the can.
Hope that helps...