The Umbwe route is a short and challenging route, which is steep and goes pretty much straight uphill. It offers the most direct path to Uhuru Peak.
However, don’t mistake short for easy as the opposite is true. You need to conquer almost the same altitude difference on any route. Therefore, it leaves less time for altitude acclimatization. Hence it has the lowest success rate.
This route is not as popular as the other routes and is really only recommended for strong hikers who are used to hiking at high altitude.