I used to have a QNAP NAS
Think it was a TS-219 or something. Nice little device, but I soon realised it was basically an ARM box running a bespoke Linux distro, and I was hitting limits fairly regularly when trying to use it as a music server, cloud backup client or whatever. Sure you could *do* most of that stuff but it was harder than I liked, and sometimes felt a bit hacky and non-standard if you stepped outside the packaged features.
Decommissioned it in favour of an HP Microserver with big cashback offer, running OpenMediaVault off a spare laptop HDD plugged into the internal USB port (yes it does work). I like OMV better; very polished preconfigured NAS experience but full fat Debian under the hood if you need to get down with some detailed configuration.
I like things that Just Work, but unfortunately I found a dedicated NAS device Just Worked for about 90% of what I needed. Other people's mileage will undoubtedly vary. Cost, while nice, wasn't a major factor.