I have only used the Stain Zone once so far with good results. I like the fact that is a one part solution as well..
Stain magic has made me look good on many occasions in the past though. I think they are both great products, it's gonna come down to personal preference
yeah I'm using both right now and I'm thinking the stain magic is a little more punch but like the stupid little 2 part sprayer because when you spray a spot your pointing the bottle straight at which causes the solution not to always pick up unless its completely full , Now stain zone is one part really cool but it didn't come with a spray head so i have to worry about what i put it in so it is vented and also finding a head just to fit the bottle without leaking all over when i tried to use it.
I think you should have both. Keep a set of Stain Magic on a dark shelf in the back of the shop, keep your stain zone in the spotting bag. If doing an estimate and you have something really gnarly, or pre-qualify over the phone if not giving estimate, and bring the SM for the bad ones. I think because Zone is a 1 part you are quicker to use it than you would be SM so it's a definite bonus.