I am both Xpenology and Synology user , the OS is great but the HW team need's to be fired .
I recently purchased an DS1520+ and well its crap for the price you pay for .
Why o bought it , because from what I see the Xpenology loaders are quite stuck and with latest updates Synology made sure it will crash those.
If you know what you are doing Xpenology is super stable. I'm using it for years and had no problems till versions 6.2.3x came out.
For my opinion Synology gives 0 crap on the hardware and proper engineering of those.
Installed also enterprise ones and still not great .
And for the 1520+ why the hell they install NVME slots when they are limiting the slots to 1x PCI-E 2.0 speed and the NVME is running not even at S-ATA SSD speed .
It's clear that the CACHE will be hurt badly in performance by this limit...
And also several devices are speed downgraded also .But NVME takes the most hit on performance when the PCI-E lanes are missing.
I attached some images from the 1520+