I have two as well. One from SU! and one from Mike's. I believe they are made by the same company. Anyway, I use it on almost every card I make! I'm a notorious crooked stamper without it! LOL.
What I also do for my wood mounted stamps, is stamp my images using my SAMJ on vellum or acetate and then keep those sheets in the case with my stamps. That way when I pull that stamp set out to use, I've already got my positioner sheet stamped and ready to go!