It can take a little while for some males to get used to the new surroundings and stop flaring all the time. Flaring is not really a bad thing and gives the fish exercise so I wouldn't worry to much about it unless he starts tearing his fins or otherwise seems stressed. Make sure he has plenty of places to hide if he feels the need and he should start to calm down.
That betta is beautiful. I have never seen that face shape... its more round than I've seen. Very adorable! All the bettas I've seen have a dip in their face.