I have used facebook app a few days ago and thereafter disabled it as it was pre installed in my asus zenfone selfie otherwise I would have uninstalled it . While using it I observed a no of issues . One with this was the loading time it took a lot of time in loading the page but the design and layout of the page is much better than as can be seen in some other browsers , one who has patience and is quality lover can wait for the page to load .
It consumes much more storage , better to use fb lite or a browser in simple , as browsers are multi functional unlike unifunctional character of fb app
Once you start fb app it automatically starts running in background and consumes a drains phones battery . In order to prevent the drainage of battery one must install hybernating apps from playstore to hybernate it and stop it from functioning in background .
Option of downloading videos is missing in fb app . Once you watch it you cant save it for ofline watching or cant be downloaded permenantly . I would like to suggest facebook to upgrade the app to provide the option of offline watching the saved videos like youtube .