Very minor issue that I've solved myself but I thought I'd report -- when I updated from 2.5.0 to 2.5.1 , it appears that my Observium NMS sync rule lost the group ID specification, so when it ran it tried to import all devices from observium and I ran out of licenses!
Easy fo fix by just updating the NMS sync group item field again, but I thought I'd report it.
Still extremely happy with Unimus, "it just works"