Yes. Yes he is.
Him together with Rashford have been two breezes of air in a room full of beerfarts that is ManU.
Player with very good technique and a lot of promise but not nearly utilized how he should be. I have been quite amazed with his close control/dribbling. He could also be quite direct with the ball (something I feel we have lacked at times) and his decision making for such a young player is quite good as well. I totally believe him leaving ManU because he is just standing still there. If he would have spent same amount of time under Poch, he'd be all over the front pages of sports newspapers. Basically he has regressed under Mou (like so many players do) - in his 1st season he scored 18 and assisted 11 while being 20. And never improved from there somehow.
But if the question is "would he be valuable for Spurs" - this one is harder. We currently have Son (last season 21 goals +10 assists; this season 18G+9A), Alli (last season 22G+13A; this 12G+17A), Eriksen (Last: 12G+23A; this 14G+11A) plus "challengers" of Lamela, Moura and Sissoko who we can deploy as AM. We still have not given proper run to Moura as of now. Would be quite questionable to slash the cash on new boy in this sense. Though I feel he would be better option for Kane substitute then Son is right now.
We have to consider that he won't go for peanuts if sold (Juve and Bayern are after him; latter being more realistic to me given the age of Ribery and Robben+ way deeper pockets then Juve), I think we are looking at around 50 mil pounds for him. So - hard to justify signing him, even though personally I really would like to see player with his qualities in Spurs.Theoretically if we could get 10 mil for Llorente and 25 for Sissoko (if we also add quality to midfield to address his departure) somehow then adding another 15 and getting Martial would make ... some sense. Though would make more sense if we'd decide to move on Lamela or Moura + Llorente. All this is extremely unlikely.