I would say if you can pick a Smarty up cheap give it a try but don't do it with mpg gains in mind. Like I said you may gain 1 or 2 if your lucky but it does make the truck more "drivable" in my opinion. My truck seems much snappier on the low end now which makes it easier to drive around town.
Again you need gauges on top of that so extra expense. EGT gauge/probe is a must and also something to watch rail pressure etc. That's why I went with the CTS, covers all of them in one package.