The Adidas Regulate boot has synthetic leather upper, whereas the Adidas Flanker boot has full-grain leather upper which is more comfortable.
The other claimed differences is that the Flanker boot has more advanced "technology" as well as a lighter sole and make up for the 8 stud pattern.
Synthetic leather is utter shite so take the Flanker which has full-grain. You'll be thanking god for that decision after wearing them a few times.