Having picked up the recent HaT releases of Von Letow's Army, I've been looking through my collection for someone to face them. How close would the Strelets Boer War British Infantry work as opponents for Von Letow? I know the earlier colonial sets are out-of-date, but it seems that this set may at least be passable for WW1.
The best ones to face them, out of what's available right now, would be the WW1 Indian Infantry. You could replay the Battle of Tanga.
The Slade Wallace equipment (pouches and canteen etc), and the Pith Helmet, on the Strelets Boer War British Infantry are not correct for WW1. The Wolseley pith helmet and 1908 Pattern equipment should be there, or, the 1903 Bandolier Equipment on the Indian Infantry.
You could get actually use the Ruga Ruga and the Askari for both sides. They changed sides, and/or used whatever equipment they could get because of the supply problems.
And some of the NNC and NNH might be useful as well.