I've actually pumped up UMs before (mainly as the french due to their high star UM gens) as well as Italians due to Tankerville and Tuscany valor bonus.

they are quite capable melee troops if you give them a little armor.

as kristaps said, in forests or desert, they acquit themselves well.

I've also many times pinned with a spear and then rear attacked knights with UMs and killed them quite easily.

once MS are up, they are somewhat obselete except for desert as Kristaps mentionned although I lean more towards clansmen and gallows as well as kens in the desert.

seems those boys fit right in across the map.