I have usually not had a problem with carry-on baggage - sometimes indeed taking two pieces (one definitely over 5kg, the other "small"). I don't remember ever having them weigh my carry-on. Or, if so, it was only under the circumstances I'll elaborate below...

Checked baggage routinely gets weighed and you will pay a modest fee if it's over. The one exception to the carry-on getting weighed is if you make a fuss about the checked baggage fee (as I foolishly did the first time I encountered it) or say, "fine, I'll take a few kilos out of my suitcase" and proceed to try to lighten your suitcase in front of them (which a lot of other international carriers have suggested I do if I'm not far over the weight limit). For some agents, that's an invitation to have your carry-on weighed, in which case you're bound to end up paying even more in the end.

Oh, I've had a bad experience with lost luggage on AR as well (bag went missing permanently - no ability for them to trace anything or tell me anything other than "wait" and then "it's gone"), particularly during busy travel periods, so if you can avoid checking, I'd advise it. My advice: put as much weight into "reasonable looking" carry-ons and don't bring attention to your carry-on(s) when you check-in. If you still have to check a bag, and it still ends up over limit, just pay the fee quietly and carry on.