Simon Sechter, famous for being Schubert's teacher, wrote this fugue as a masterclass in strict counterpoint. It highlights his deep mastery of harmonic and contrapuntal rules.
At Henle 6 this is an advanced piece that assumes fluent technique and rewards mature interpretation. The main demands: independent voices that must each sing on their own line; a left hand with real melodic or rhythmic responsibility of its own; and chord voicing — bringing out one note inside a handful of others.
Beyond that, expect a true singing tone, with the melody floating above the accompaniment.
Focus on the smooth, connected voicing required to bring out the dual subjects in a lyrical manner.
Comparable difficulty and character — good candidates for what to learn next.
A level or two down with the same spirit — ideal if this piece is still out of reach.
Where this piece's skills lead: slightly harder works making similar technical demands.
Double Fugue in E minor is rated Henle level 6 of 9 — advanced repertoire, roughly ABRSM grades 7–8. In the RCM system it corresponds to about level 8.
You should be comfortable at Henle level 6 — meaning you can already play level 5–6 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 Double Fugue in E minor lasts about 4 minutes.
Double Fugue in E minor 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 Ballade en mode phrygien by Jehan Alain, 12 Variationen über ein eigenes Thema by Alban Berg, 12 Variationen uber en eigenes thema by Alban Berg — see the full similar-pieces list on this page.