"Safe" is a subjective term...the fact is that Adobe hasn't released an update for Flash since last August, which means that any security exploits discovered since that time have *not* been patched. Not being an expert on the subject myself, I can't speak to what security holes, if any, do exist for the latest Flash .apk, or to the perceived risk or severity, but given the history of Flash it's probably a safe assumption that the working versions of Flash that exist for Android do have unpatched security vulnerabilities.
On top of that, fewer and fewer Android browsers work with existing versions of Flash, and as the browsers are updated and Flash is not, that compatibility list keeps getting shorter and shorter.
I understand the desire to get Flash loaded, and frankly it stinks that many Flash-enabled sites don't provide content that works on mobile platforms, but at some point we as users need to accept the fact that Flash for Android (or any mobile device for that matter) was a failed experiment and is essentially dead. I personally wouldn't recommend loading a 9 month old version of Flash that was never designed to run on Android 4.2 to begin with...but yes, it is possible (for now) to do so if you really need it.