IMO very good move by the football club.
The Dons set up in the same formation as Everton, play passing possession based football built from the back, and more importantly rely on the one striker up front.
Since the departure of Patrick Bamford, who played nearly every minute of every game this season, the other striking options at the club are extremely restricted, so Long will be getting a lot of game time I believe
Seems like a sensible transition to build him up for not only first first team football, but to do so in a way similar to what he can expect back at Everton.