Was using it several years ago, found it to be more trouble than it was worth. Now I just try not to mess things up!
My particular setup undoubtedly contributed to my situation. So, a little info on the "more trouble":
The cheaper guns a I got could not provide the needle-sharp spray that I'd experienced with a better gun in my first shop. I had no vacuum stand/evacuator. These two factors meant the shirts became quite saturated with chemical, risked bleeding into design area, took forever to dry, and only sometimes was the spot effectively removed. And yes, 1 gun died, got another one. It didn't perform much better. I finally just didn't replace chemical one it ran out.
That said, in the previous shop, with a better gun, a vac station, and much higher production, we used spiff often. But it was the old stuff that would remove paint on contact if you spilled it.