[itsme]

My proposals for improvements
1.) allow switching between "by key" and "by semitone"
This can easily be achieved by changing the labels on the existing "Transpose" window: replacing C ... B with 0 ... 11 and labelling the buttons "b" with "-" and "#" with "+" would fulfill Sciurius' request.
Alternative: a slider -11 ... 0 ... +11, no buttons "b" and "#"
Close to transposing would be better than in the general settings, e.g. a button in the "Transpose" window or two items to select either "by key" or "by semitone"

2.) decision if sharps or flats are used
A decision by MSP is only required if transposing is activated. I think it is wrong that MSP in the key of C displays always e.g. D# when Eb is found in a song file. With no transpose it should show what is found in the file. 
When transposing is activated, it is required to decide if sharps or flats are used. MSP (and probably all other ChordPro readers) can only decide this per song, not per individual chord. Currently the destination key specifies the usage of sharps or flats in MSP. That is ok in many cases, but not for all. I agree with Sciurius that it would be far better and easier to read if I could specify my preference for flats or sharps per song. That happens more often for destination key C, but is also useful for other keys. Note: we are talking about the chords, not about single notes.

3.) detect the starting key
To know the starting key is mainly required for transposing "by key".
The UI to specify the starting key is unnecessary and confusing. That should be removed. The starting key should be detected only by the content of the file. We have "Detect Key By" in "Text File Settings" to start with. If the file contains a "key:" tag that shall overwrite the result of "Detect Key By". That's fully sufficient.