Real mules?

Real mules are faster, probably quieter, and carry heavier loads than this thing. So why don't modern infantry use them? Because they're a ridiculous idea, that's why. Either you're being stealthy, in which case sorry but you need to carry your own kit. Or you aren't in which case, throw your kit in the back of a 4 tonner, warrior or quad bike.

Gloriously Belize have a mule load as a standard weight measure. It's 200lb.

http://www.sizes.com/units/mule_load_standard.htm