Safer in what way?
If you install PlayOnLinux from the Linux Mint repository (which for this package is actually the Ubuntu repository), any emerging security threats will be managed by the Ubuntu security team. If you install it from some other repository, you will depend on the maintainers of that repository to handle security threats. For which they may not have the same experience as the Ubuntu security team.
Installing PlayOnLinux from the Linux Mint repository will ensure the program is compatible with other programs from this repository, such as Wine and other dependencies for PlayOnLinux. Installing PlayOnLinux from some other repository, you will depend on the maintainers of that repository to not break the package by including dependencies that can't be satisfied on your version of Linux Mint.
Are either of these big issues for a Wine front-end? Probably not, but that is the difference.