This work likely takes a traditional German folk melody and subjects it to variations characteristic of the Classical period. Cramer's approach would involve clear melodic development and elegant, often virtuosic, piano textures.
Maintaining clarity and precision in scalar passages and Alberti bass figures is important.
11 Variations on a Saxon Air, M.6.09 is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 6.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 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 11 Variations on a Saxon Air, M.6.09 lasts about 8 minutes.
11 Variations on a Saxon Air, M.6.09 is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.