The maul seems significantly stronger to me, especially at the end. That fear effect can be wildly strong. My battle master was a beast with Menacing Strike (it imposed fear) and that was only usable up to four times between rests, whole you've got this usable every round.
And having +1d6 on every attack is probably closer enough on par with the multiple heads of the flail usable occasionally, that the fear effect is a complete bonus, I would predict it overwhelms the advantage once per round the flail grants.
Ultimately, my suggestion would be to change the maul's fear effect: I'd give the maul 7 charges. On a hit, the weilder can expend a charge and the target must make a Wisdom save (DC whatever) or be afraid. Etc, as you've got written.