Yamaha arrangers & If I remember my Korg pa3x have ONE TOUCH Transpose +/- on the fly which is great.
but Roland arrangers I've had G70, etc, is a two button execution

which is much more difficult in real time for a split second modulation etc.
The G70 is the simplest...2 buttons one for up ..and another for down...and is lit when transposed..
Personally, I rarely use the transpose feature..I am comfortable in most keys..
Why is it though...my vocal keys always seem to be in the keys "B" "Ab" and "C#"

My favorite playing keys are "Eb" "G" and "F"