Earlier quoted context omitted.
It still works, you just have to fight it steering you to the app store every step of the way. I had to borrow someone's phone 2 days ago to send a quick FB message and it took about 10x longer than it should due to it trying to hide the native interface "it's going away soon, install messenger".
Is this an Android vs iOS thing? The Facebook page on my iPhone works very similarly to the desktop page. It doesn't steer me to the app store for any features.
It may be, this was in Chrome on an Android phone. Go to the inbox and it'd pop up app store. Close it, and the browser would be displaying the message about soon having to install messenger instead of inbox. Close that message and the process would repeat.
Only by visiting my friends profile and hitting the message link could I actually break out. It'd still take me to the app store but on close my friend's messages were visible along with the box to send a message.