I have actually played an alto trombone, but not very well and for one performance only ... but this piece is just great ...
It's very characteristic of the classical virtuoso trombone style. As a composition it could make a popular addition to the repertiore - I'm not aware of any comparable modern alto trombone pieces, though I may well be out of touch.
The actual trombone sound you've achieved is impressive and the detail in the articulations is astonishingly precise and accurate to how a real player would have to play your piece ... you've managed to push it to the boundaries of what is reasonably possible on a trombone without going over the limit and giving the game away to those in the know that it's not a real player.
It's so annoying when you see a film, say, with someone supposedly playing an instrument you're quite familiar with and there are fundamental flaws which spoil your enjoyment ... but your piece is utterly convincing and [almost!] flawless, and very enjoyable!
Just one question, though ... as an Englishman I don't understand the title ... could you explain, please?