The update went well on my FP2 with encrypted data partition and multiple users. No data or configuration seemed to be lost, also no reboot problems.
There was one problem though: I wasn’t able to connect my Pebble 2 smartwatch to the Pebble app on the phone. The Pebble 2 is special compared to other Pebbles (or even other smartwatches) as it only supports BLE (Bluetooth Low Energy). I didn’t have any problems with “normal” Bluetooth connections. So I wonder if there are other people who had problems with BLE connections with FP Open 17.06.04?
I am not sure if the following info is useful: The BLE connection with my Pebble 2 worked well with the previous version of FP Open and it also works well with LineageOS 14.1 (which I just tried).