Sorry but had quite the opposite experience even with the professional lines. The only NAS i trust is a Server (at least HP mini server) and ZFS. Stuff like unraid is for Windows mindsets, i don't trust HW-Raid and i especially don't trust Closedsource Software BS for stuff like that, exceptions are Enterprise stuff like EVA's or NetApp and EMC.
This is how you'd mount a synology array in a Linux server: https://www.synology.com/en-us/knowledgebase/DSM/tutorial/St... - it's basically two terminal commands after all the preparation stuff.
I believe QNAP uses mdraid as well but I haven't had any experience with those.
Yes and that raid destroyed itself many times which btw never happened to me on a self-installed Linux.
I'm sorry you've had the misfortune of encountering such problems.
I've been using Synology/Xpenology (a fork of their GPL bootloader) for 8 years, and it's still going great for me.
Btrfs is on the kernel and just works.
Otherwise, e.g. Synology produces excellent devices, etc.