Do you know how good the quality is when doing the phone calls?

Can it dual boot?

It can triple boot :)

Any of the following, if I'm not mistaken:

Android / Android rooted / Debian / Sailfish / Kali

Very tempting. Having it as an Android phone most of the time, but rebooting into Debian to mount other peoples' devices or do video out sounds like the kind of device that might finally make me switch from my iPhone 4S. I don't need the physical keyboard though, and I'd want a USB-A port and HDMI port instead of USB-C for everything. So perhaps there are other devices that might suit me better. Still, it looks very attractive. Kind of like the OQO Model 2 I used for a few months before it died on me.

>my iPhone 4S

That hasn't been secure to use on the internet in a long time.

It's certainly listed on that webpage as a feature.