This probably falls under "capabilities", but another consideration worth strong consideration is
mobile network support. With the past phase-outs of 2G/GSM, ongoing 3G phase out, converstion to LTE and VoLTE, and expansion of 5G networks, as well as differing network and frequency standards around the world,
finding a device which will work with your preferred mobile provider(s) is a challenge.
This is one of my strikes against the Punkt mp02: it doesn't work with most of my carrier options. I was hoping that either that device's capabilities would be extended, or its replacement would follow a similar ethic and expand bandwidth / protocols, but neither occurred. Further reading on Punkt's offerings has further cooled my interest (bugs, fragile HW, spendy).
RCS and group chat support seems to be another sticker, though with a small-form-factor laptop or tablet you should be able to work around that.
The other sticker for me (mentioned in my original post) is voice/SMS/messaging filtering options. The increase in spam / unsolicited contacts across the comms spectrum is immensely frustrating, and few devices / OSs / apps really address the situation adequately and in a privacy-respecting manner. That's still giving me a lot of hesitency on what really ought not to be this complex a decision, though for now I'm thinking it's a good thing to spend the time.