Is something like that just for when your car is throwing codes or will it tell things like knock counts and such? Basically if someone could just give me a basic rundown on the info it will supply. Since i live on a military base i can have this done for about $10 instead of like 50 or 60.

 

For $10, I'd go do it... see if you can get a printout. But for the most part, a shop will only get at any stored error codes. It'd be rare (and cool!) if you found a mechanic that said something like "Hm, the IAC counts are a bit high, let me look at that." To most guys, no code = no problems.