I can't find comparisons between the Mendoza and the Sten, but I do see claims that the Mendoza was more accurate and more reliable than the (German) Mauser. The Sten was designed to be very cheap and easy to produce, which it was, with no complex or precision parts; but it suffered from being unreliable and flimsy and did little to inspire confidence in it's user. so (one could conclude), if one could manage (somehow) to get the ammo....