It's good to get other opinions here, and it's certainly interesting to hear arguments for out-of-tree drivers.
But one very important question comes to mind:
What happens when you no longer support that hardware? What happens if your company goes bankrupt, reduces in size, etc, and can no longer support the out-of-tree driver?
You then end up in a situation where users cannot ever upgrade their kernel because your out-of-tree driver is no longer being upgraded.
I worked for a company that has an out-of-tree driver. We ended up only officially supporting quite an old kernel. This screwed over customers that needed a newer kernel (typically for newer power management features)