Hey Eddie, I've owned quite a few tangs, and IMO the ones you're looking at Tomini, Yellow, Kole, Bristletooth, Purple... seem to do more grazing than swimming.
I owned a Kole and a Yellow, and they never really bolted across the tank... more just floating from rock to rock picking at the algae. Both of the ones I picked up were 3" or less at purchase time. Misled's new Yellow Tang is my old one.