Betta Fish: Is it bad to flare often?

Hello! This is my first time posting in this subreddit! This is also the first betta fish I have owned since having one as a child and doing no research and definitely not a proper set up. I have come a long way in my fish knowledge journey as I currently work at a pet store and always strive to give the best advice I can. I’ve recently set up two tanks, a 10 gal. started at the beginning of Feb and is now cycled, and a 6.8 gal. started about a week after and about a week until it’s cycled. We recently received this halfmoon-rosetail betta in at work and I fell in love with its colors and anytime we had to move his (unfortunate ik but recently upgraded to bigger) cup He HATED IT and would bonk himself around everywhere, I am unsure if this is something neurological or just standard betta cup keeping behavior. Knowing I had a tank set up and safe for inhabitants I really wanted to get him out of there. I brought him home tonight and have him in my 10 gal, and am going to move him to the 6.8 gal. once it is fully cycled and ready. I’ve noticed that he can see his reflection in the HOB filter thats in there and am concerned if him flaring will stress him out in a new slightly larger tank and be too much? Any advice would be greatly appreciated! Also this is Lettuce in all his glory!