and Man Utd will officially offering €120 millions for buying him
He could be another disappointment like Di Maria, but that only has a tiny bit of chance of happening. Bale has EPL experience and was doing an excellent job with Tottenham before he moved to La Liga. IMO a player moving from La Liga to the EPL will have a much difficult time adjusting, maybe due to the weather, the tougher competition and various other reasons. In La Liga on the other hand, it is a much easier league to adjust in for a player as there are only two clubs competing for the title year in and year out (ok 3 with the emergence of Atletico).
So Bale going to La Liga did have some adjustments on his part, but nothing he cannot handle. Di Maria to EPL had a much harder time adjusting, and it didn't help that their manager is LVG too.
The weather and tough competition arent a problem for La Liga players to play in Premier League, it has been proven by David Silva, Juan Mata, De Gea, Bellerin, etc. Even La Liga team can win in England in some UCL matches. The only problem is how the club and manager treat their stars. Under Sir Alex, Man United rarely bought expensive players, so we can say there is no burden for every new players he has brought. But after Sir Alex retired, there are few expensive players, and their fans surely expected them too much than usual, it's a burden for them actually. Look how bad Falcao and Di Maria play, not because they are bad players, but the club can treat them properly. With that high price, the whole club assuming the players can play in every position, but they can't. But, now Man United have Martial, a young player with high price, and the best part is he can play in every position van Gaal set. I suppose he will be a superstar someday.