From what I've seen of Hannibal he hasn't done anything extraordinary in the first team yet. But he's done okay.
Ya. His energy and willingness to get stuck in mean the fans will want the best for him. But nothing yet to suggest he could tie down a first team spot at all - not to mind for a decade.
As for Mainoo, the reports from the summer pre season games before he got injured were that he was United's best player. Had some 115 million pound nobody in his pocket in one game. Can't remember the fella's name to be honest.
Looks very nippy & tidy in the little bits I've seen of him - but United are well familiar with pre-season Pirlos.