We caught wind flow of an FCC filing for your ZenWatch 3 the other day with the interesting quirk— the tag was round. That would indicate a round watch, but the device was being kept confidential. The Chinese version from the FCC, known as TENAA, had not been as careful and has leaked images of the ZenWatch 3 in all its round, grainy glory.
Therefore , clearly this is indeed a round watch. Asus went with a three-button design, such as the most recent LG Watch Urbane.
Asus ZenWatch 3 images leak through Chinese regulator was written by the awesome team on Android Police.