They're both Fenders with four strings, a body, and a neck. That's about all they have in common. A Mustang is short scale. The Fender Jags with all the controls are regular scale. A Mustang has one split pickup, tone & volume control. Beyond that, it's a matter of what you prefer as a player.
G-K club # 602, Short Scale Bass Club #159,Squier Jaguar SS Bass # 15, Trinity House Mudslinger, OFBPOAC #23