The Brits call the M16 series "Armalite" because that's who they originally bought them from. So when a Brit troop says, "Armalite" he's talking about the AR-15/M16.
Originally the "Armalite" was used to replace/supplement the Sterling SMG in the jungle. So most troops had the L1A1 (then itself quite the new weapon), and guys that would normally have had the Sterling had "Armalites". The Australians did the same thing with the Ownen SMG in Vietnam. They replaced them with M16's. The "Armalite" was pretty popular because of it's weight, and because it was much more effective than the 9 mil.
The same reliability problems cropped up in Borneo that would later plauge the M16 program in Vietnam. You don't hear about the M16 in Borneo much because the US wasn't there, most troops actually had the L1A1, and on the whole the "Armalite" was better maintained by the Paras and SAS, than the drafted US rifleman of VN. I've seen several pictures of Brits armed with "Armalites" who taped assembled cleaning rods to their handguards so they could pop out stuck cases. This seemed fairly common, as it wasn't the same guy or even the same unit (both Para and SAS). That would indicate that the reliability problems were widespread enough that it wasn't an isolated case, and that they delt with it the best they could. Why the US didn't look at the British experience with the rifle and at least issue cleaning kits when they bought them is another matter. In the end we threw money at the rifle and came up with fixes for most of the problems.
Ross