Kate Loder’s cadenza for Mozart’s 19th concerto is a rare nineteenth-century contribution that attempts to bridge the gap between Classical conciseness and Romantic expansion. Its rarity makes it a unique historical artifact in the performance tradition of Mozart concertos.
The player must maintain a light, Mozartian touch despite the more active, idiomatic Romantic passagework present in the cadenza.
Comparable difficulty and character — good candidates for what to learn next.
Cadenza to Mozart Piano Concerto in F, no. 19 (K. 459) is rated Henle level 7 of 9 — late advanced repertoire, roughly ABRSM grade 8 and above. In the RCM system it corresponds to about level 9.
You should be comfortable at Henle level 7 — meaning you can already play level 6–7 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Cadenza to Mozart Piano Concerto in F, no. 19 (K. 459) lasts about 2 minutes.
Cadenza to Mozart Piano Concerto in F, no. 19 (K. 459) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Sonatine by Maurice Ravel, Partita No. 1 in B-flat major by Johann Sebastian Bach, 12 Variations on 'Je suis Lindor' by Wolfgang Amadeus Mozart — see the full similar-pieces list on this page.