I'd say theymos'
I'm not going to lose sleep over people more or less applies here. My own personal opinion: it's 3 Merit, it doesn't matter. The Legendary user has earned a thousand times more than that already, and he's not even using an avatar or longer signature on his cellphone account. I don't know the reason why he Merited his own alt, and in my opinion it's better not to do that, but in the grand scheme of things, it's insignificant.
But he is still using his main account to give positive feedback,
this user got three positive feedbacks from his main account and his alt. I don't think this is correct use of trustlist and trust feedback from my understanding so far.
Agreed. Nobody should bump someone's feedback score by more than one point (up or down).