I play music by sight (poorly) and can improvise a little bit on guitar, and would love to understand music theory better but so far do not.
Is this a useful device to get a feel for creating music, or is it only really useful if you already understand music theory or improvisation?
Additionally, understanding theory and improvisation is certainly a great thing to know if you're trying to make music, but you can understand a ton of things in the abstract and also be pretty terrible at applying it in the moment.
So if you want to get a device you can throw some hacked firmware on and have some fun, I'd say don't let your lack of theory hold you back.
"Useful" is a really subjective word when it comes to making music in general. Some template groove on a shit keyboard could be the base for a hit song (like Gorillaz' Clint Eastwood) while others don't make stuff unless in front of a modular synth with 100% control of everything.
Any instrument can be fun without knowing music theory, as long as you're willing to trial and error for a bit, until you find what sounds good :)