ECC support depends on the processors that the NAS uses. A few of their NASes allow you to use ECC memory but you'd need to swap the memory installed to ECC memory. A lot of their systems use Intel cpus that don't support ECC at all so you need to carefully pick and choose.
Some of them use arm based CPUs from Amazon’s Annapurna Labs.
> You can not take a zpool out of a QNAP system and access it on another system with ZFS.
Too bad... I always wonder why companies do this...
Some do. I got the TS-873A a few years back, it works. Their software is kind of weird, and I wouldn't connect it to their cloud offering, but it does work.