Gotta give props to LVG for only needing a week to get not one but 2 XIs to play in a formation they've virtually never used, and at least not look uber-confused.
But, I'm not sure it's a long term good idea. As smart as LVG is, is he that much smarter than every manager that has coached in the prem for the last 20 years? Because no one has been able to get a 3 at the back system working well in modern premier league era, not that I can think of anyway (and by well I mean challenging for the title). I'm not a FM/tactics guru but I am a stats guru, and so just looking at the numbers, there's a lot of evidence that 3-5-2, for whatever reason, doesn't work in England.
That said, seeing Mata play behind the forward line, in a pocket of space...it was so beautiful
One thing you should be able to give United players is tactical flexibility. Towards then end you had literally no f*cking clue what Fergie was going to ask them to do each week. Stick a striker as a holding midfielder? Okay. Fullback and a winger in central midfield? Sure. Two fullbacks as wingers? Yep. Midfielder as centre backs? Sure.
So maybe they will be prepared and able ot switch formations week in week out. Would be impressive.