Hi Rob,
The difference is in the analysis. MIK analysis algorithm has the best so far. Every year it is tested annually MIK comes out on top. The KEY is written in the tag that is meant for it. So whatever program analyzed this, the value is written in the same place.
With MIK are you sure that the KEY is correct. Pioneer will say their software is as good but like I said, the test proofs this every year.
What you should know is that the MIK notation is not always displayed in every player. In RB this is still displayed, that's no problem.
You mentioned above,below,left & right for matching the songs, there are many more opportunities though, +2 (+14) and + 7 for example. Buy the book "http://www.mixedinkey.com/Book/" and there you will find more information.
Tom