We've used it in 16 persons raid the past two nights. While I enjoy the interface and improved metrics, connections are definitely an issue. People are randomly being included and excluded for certain encounters, randomly showing up in groups alone, being listed as "linkdead" when they appear connected on their end, etc.
We've identified an issue that could be causing this, look for an update in the next day or two. We will also be improving the troubleshooting functionality to work within an already formed group to help identify what may be going wrong with this or other issues. In general though, MoniTOR should work for 16 man operations without a problem, that's the size operations we run most nights in my guild where it was beta tested.