We know that holding Bitcoin is better when users have full control over their funds. What makes an open source software better? Is there any advantage on using it than using close source wallet.
With a closed-source wallet, you have to wonder whether it's been sufficiently reviewed. Further, it's possible your private keys could be stolen and relayed to a malicious party. While the latter is unlikely in the case of a reputable company like Jaxx, it's still a potential way to lose your coins.
Stick with an open source wallet that's been extensively peer reviewed.