I am really liking the Bb key. It is a little dark and moody, which is more my style. I am very much not a fan of the whole perky island vamp sound that is so connected with the ukulele. The only thing that doesn't quite work is the I IV V progression. At least with a linear tuning it sounds a bit off. The Eb inversion sounds out of place (too high). I didn't notice this when playing a re-entrant tuning. It still works but it is a little idiosyncratic.
I was playing the Bb melodic Aeolian and making little songs. I really like moving from the Bb to the F in syncopation, and then running back up the scale. It sounds kind of like a Russian march.
I practiced the Bb minor pentatonic as well. Since I'm playing linear I can get three octaves although the latter part of that run is made by sliding down the A string since I've run out of room.