This is another contrapuntal setting of the chorale, likely an early or sketch version. It shares the intellectual rigor of Bach's other fugal works, though perhaps with less polish than his mature compositions.
Focusing on the contrapuntal independence of the voices and precise articulation is essential.
Allein Gott in der Höh sei Ehr (BWV 676a) 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 Allein Gott in der Höh sei Ehr (BWV 676a) lasts about 4 minutes.
Allein Gott in der Höh sei Ehr (BWV 676a) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.