You can read a fair bit of data from an OBD II reader. By law, they have to allow access to anything emissions related.
So TPS, IAT, O2, AFR, Knock, Trims etc. Been a while since i plugged mine in, but theres a fair few. It wont do everything the Kpro reads off of course.
I was dead set on a Kpro, as Id fiddle with it etc, play with crossover, all the fun stuff. In reality, i knew id play for a few weeks, and barely touch it.
But Paul explained a lot of what i wanted to fiddle with, was part of / would affect the map.
Sure, they look pretty on a nice HU display, and to impress friends, but very few people will be doing anything other than looking at generic sensor data.