This is the most important part of the process. You need a version that specifically supports Android 4.4.4 (API level 19) as the minimum requirement.

Go to Settings > Apps > Messenger and tap Clear Cache if the app begins to slow down over time. Troubleshooting Common Issues

Using an outdated version of any messaging app carries inherent risks:

No. Rooting is not necessary for sideloading a standard Messenger APK. Only enable Unknown Sources.