I've been using UEB for a while now, and it's been pretty awesome. Occasionally we run into issues with backups failing, but that has mostly been fixed with configuration tweaking.
We're looking to expand our storage used for backups, but seeing as UEB adds storage to a common pool, what happens if one of the attached VHDX files becomes lost/corrupt? ** The answer is yes, it becomes lost, as highlighted in the documentation. Silly me for not seeing that. **
** Also, not to hijack my own question, but is there an explicit guide for how/when the incremental forever decides to create a new synthetic full? They keep happening well before our max retention age. (I'm pretty sure it has to do with how much storage is free.)