A good tuner is typically the best bang for the buck mod you can do performance wise.
The superchips for the 2008+ 4.7L provides tremendous power increase. You will see nearly 70hp and 70lbft of torque increase on the 93 octane tune(MAX gain, not PEAK gain), and IIRC it's about 50-60hp increase on the 87 octane tune. It is a huge difference and pretty noticeable. And this is not BS, superchips posts dyno's on their site.
Aside from the power increase, you get to adjust other things like rev limiter, speed limiter, shift rpm, torque management, and for an additional $40 or so can buy advanced trans control and make your own shift schedules. Plus the other things you can do like adjust for larger tires, etc.
As long as you don't reduce torque management to 0 or next to nothing you will not cause any harm to your truck. I know a lot of guys who have been using diablo and superchips products for 100k+ miles and longer with absolutely no issues. And some of my buddies really beat the hell out their vehicles.
Personally, I use the superchips on my 2010 4.7L and love it. I have 80k miles. I don't beat the hell out of my truck but I use it and have fun in it. The only times I've seen issues/damage from tuners is when torque management is drastically reduced or completely removed. And this is typically only the guys that have wild mods, turbo, nitrous, etc.
Get it, you won't regret it
*also, although it should increase mpg slightly, I wouldn't count on it. Don't expect it because everyone seems to see a difference here. Some claim no change, some claim 3mpg increase. Just get it for the power, driveability, etc, and don't expect more than 1 mpg increase and you'll be happy.