I've used it for a while, even before it was a forced usage and I like it. I only want messaging from Facebook most of the time so having it separate is great for me.
I still don't like the fact that I have to have two Facebook apps on my phone. However, it is nice when I deleted the main Facebook app and only had Messenger. I was still able to get messages from friends, even though the primary FB app was not installed on my phone.
It doesn't bother me really. I just put the messenger app in a folder and forget about it while using the main Facebook app on the home screen. It is whatever works for you really. Its not like a minority of people refusing to download the app is going to force Facebook into changing anything. Whatever innit.