The Smarty makes nice smooth power and is supposedly undetectable.
If I only had 1 box it would be the TST. It'll make as much power, gives you better control over timing, pressure, ramps, etc. Gives you a free cooldown timer and high EGT backdown as well as built in gauges and most importantly the ability to turn it up, down, or off on the fly from in the cab.
Personally, I use both.
-Scott