If we sign Mkhitaryan, he would be our first properly two-footed attacking player since Nani, and his versatility would be great to have. He's also not too old at 27 to be a key part of our building plans. He also shares an agent with Zlatan, so there's reason to think they're at least familiar with each other, if Zlatan does indeed come.
He is not very quick, but definitely smart and a good finisher. He's had a really good last season, but before that he was infamous for not being able to score, last season he got 23 in 51, before that in the previous two seasons he got 17 in over 80. I don't think he is one of those classic wingers, he is converted one (just like Mata, but obviously better than him playing on the wings).
30 million Euros is definitely cheap for a player of his quality, but if we have an option for signing some one like Mahrez for 40m, I would be tempted to go for him instead.
From Mkhitaryan's perspective, he would be better of signing for United rather than Arsenal, as there would be almost no competition for his position in United's squad.