Yeah, I have the cart and also a memory card thing for homebrew apps (there are some other good DS music things like GlitchDS etc), I’ve taken to loading up multiple folders with duplicates of the DS-10 so i can have more save slots 
one of these days i’ll actually finish one of the grime or flashcore tracks i’ve been trying to make while on long train journeys
(likewise with the iphone nanoloop too)
Oh cool, I have used ipad version of the MS-20 which is pretty great too