I personally upgraded QNAP hardware for SMB clients. The process couldn't be any humanly simpler.
Just swap hard drives from one to another, keeper the order. THAT'S IT.
The new device kept ALL of the settings, installed apps, and of course data. I didn't have to correct or change anything, not file shares, network info, or a native cloud backup setup.
As much as I love QNAP for Personal/Soho/SMB cases until they could match the level of support iXsystems provides (which I could personally attest as their paid customer is great), I'd recommend iXsystems storage as second-tier storage over Qnap/Synology every time.
As far as these units price, I agree with Patrick- these are well-engineered machines using modern and high-performing parts, but hard to shake off the feeling that the prices are a bit too high. I am not saying that the alternative is to roll my own NAS, but feels like QNAP as the sole provider of NAS with modern hardware has cornered this particular NAS market corner all by itself and free to set its own prices. Maybe if Synology, Asus, Netgear, Buffalo, WD, and Lenovo would update their NAS models maybe we would some healthier competition, but given how still relatively small the NAS market is I highly doubt it.
I give you an example that is close to me:
Subwoofers - A very well-made internet direct company Subwoofer starts around $800-1000. To make your own sub including, the wood, driver, amp, possibly some DSP module and its nice-looking finish would likely cost very similar, maybe savings of a couple of hundreds, but that still doesn't take into account the required tools. Some bigger savings could come if you build monster-sized subs and more typically pair or more.
On the other hand, building your own DIY NAS (especially from used parts) could be drastically cheaper (typically sacrificing noise and power) - I mean not crazy to build a high-performing 12 bay NAS using an old HP DL380G8 server parts well under $500. A comparable performing unit from QNAP would be easily 3-4 times the cost.