Reading his Wikipedia entry this stood out for me and summarises why I think we should be OK with this contract extension:
"He made his debut for the club on 14 September, in a 2–0 home win against
Crystal Palace, coming on as a 62nd-minute substitute for
Anderson";
There is an irrational tendency to dislike some 'squad' players on the Caf but the fact is that, as the Fergie years should have taught us, squad depth and player management are key for successfully challenging on several fronts concurrently and that is where Manchester United aspires to be. Mou knows this even if we fickle fans chose not to see it.
In the past players like Anderson, who was also happy to sit on the (straining) bench, have been loved by the fans seemingly for no other reason than a jolly disposition. Fellaini is a combative and reasonably skilful player who keeps fit, always gives 100 %, doesn't grumble about often being a fringe player and who chips in with the odd (and vital) goal.
There is also an element of being tarred by the Moyes brush of incompetence here: It is not Marouane's fault that dithering Dave managed to pay more for him than his release clause and then did not seem to know what to do with him once he got him into the club.
At the time of his signing it was well documented that Fellaini had forgone some payments he was due in order to get the transfer pushed through but he has garnered no good will from this, the association with Moyes seemingly being too damning in most fans' eyes.
He is an international level player with multiple caps (and goals) for a quality Belgian side. He has qualities that no other player in our squad has and brings a plan B to the table that otherwise we'd lack - witness the second, possibly decisive, goal in a semi-final this week.
Yes he looks like a cross between a bog brush and jar jar binks on ice sometimes. You try not looking as awkward and uncoordinated as Peter Crouch occasionally when you are 6 foot 11 or whatever he is. Yes he looks rusty and struggling to keep up with game pace sometimes. He never gets much of a consistent run in the team after all. Get over it - he is a decent squad player and has done more for United than Morgan Schneiderlin (or Anderson) ever did and I for one think we United fans should give him a break.