As I've said elsewhere, I would be slightly underwhelmed, personally, not because he isn't a very good player, but because he isn't obviously better than what we already have at the club, and I don't see him improving to the extent that he ever will be, even with the inevitable improvement that comes with playing with better players and in a better team. If there was a real need, as there was when we signed Valencia, for example, then I would be much more positive, particularly if very few alternatives were available at the time.
As an alternative to both Nani and Valencia, he is obviously a very good player indeed, but if he isn't ever going to improve to the extent that he eventually replaces either of them, as could happen if we bought a young player with that kind of potential, it leaves the impression that the club is somewhat 'standing still', rather than looking for players of the absolute highest quality for the future.
Young is of a similar quality to Valencia, in my opinion -- i.e. never likely to become one of the best players in the world in his position -- but he would at least offer certain qualities that are lacking in the games of both Nani and Valencia, and he is probably more comfortable on the left hand side than either of them, despite being similarly right footed. As a player, then, he would certainly improve our squad, which is a plus point in itself, and he may prove an intelligent signing for a relatively small transfer fee, particularly if money is to be spent elsewhere on the team.
If that were to happen, then the signing of Young would make a lot more sense, but I would still rather that we looked for players with the potential to improve on what we already have at the club, unless there is an obvious and/or urgent need.