Here is a piece I have had in my collection for over 30 years; a Capriccio by Handel.
Years back , I copied it from a transcription meant for flute, and changed it to another key. It is really great to play it, as it is moderately challenging, with having semi-quavers all throughout, and yet can be managed with a bit of care and practice. It keeps going and then ends with a sort of flourish.
My flourish I added is a huge "trill "..using the bellows themselves to quiver the last notes [ great fun to do]!
I play it lower than my written transcription I referred to, and with a couple of altered notes as I went along.
Very challenging on concertina to get the bellows air in and out at the right moment too! I like to think good old Mr. H might have approved; after all concertinas are miniature organs [ and he was organist too]😊!