I have a scan tool already.
Most of the lower end (mine was around 100) just read codes, and freeze frame data (9 or so values stored in the cars computer when the code is set).
It also came with a software package and I can plug it into my computer and download that data, and it has a program with details about individual codes, likely causes, etc...
However, after visiting with thefatkid about a problem on my 99, I saw the advantages of being able to watch what is going on in real time, and see all of the sensor inputs.
For example, my dads code on the 04 taco was P0171, Bank 1 Lean.
This has quite a few possible explanations: Bad or Dirty MAF, stuck throttle body, leaky injector, bad injector, bad O2 sensor, and a few others.
My reader simply told me what the long and short term fuel trim were at the time of the code. My software listed out the specs they should be (within + or - 15%), and since they were both above +15, I could see the reason for the code. However, that doesn't tell me WHY. If I could monitor everything in real time, I could see what he MAF and O2 sensors are doing so I could see if one of them was simply giving bogus values. I could also monitor the TPS and see if there were any issues with a sticking throttle body.
I had to do the ol guess and check. I reasoned that they live on a dirt road, and therefore it was a good possibility that the MAF was dirty. Sure enough, it was filthy. Cleaned it, but while I was in there, I noticed the throttle body had a ton of carbon inside it, so I removed and cleaned that was well.
Anyway, that is my interest in the extras. It really does allow for a much more in depth diagnosis, and, IMO, less time overall fixing an issue. To me, that is worth the added cost for the extras.
Baby Beast 2- 1999 4Runner SR5
Baby Beast -1987 4Runner SR5-Gone, but not forgotten