I find it important especially in rehearsals to be able to just explore new ideas quickly. I found I don’t really need a full “swiss army knife”, but rather get by with a couple of quick basic setups. I have four “keyboard” rehearsal songs, all based on one basic sound on my lower keyboard, and a range of four additional options on my upper.
Lower keyboard determines the song to be loaded: Grand Piano, Wurly, Rhodes
Upper keyboard gives me 4 options in song states: Rock Organ, Blues Organ, Sax, Brass
The fourth song is a two-manual Hammond organ between lower and upper keyboard.
Plus, I have a guitar amp song for when I play guitar, with song states from clean through to high-gain.
That gets me through most rehearsals when I don’t have the time to actually prepare a dedicated Cantabile song for new material.
When I really need to get more complex on-the-fly, I have my “custom overlay” project, but TBH, I’ve only needed it very few times so far…