The #MEGA65 and #spectrumNext are limited production runs AND expensive. The Commander X16 will also fall into this category when it arrrives. The #Foenix256 is much of the same IIUC.

The #AgonLight is cheap, always available and does just enough to be useful and whilst there are other SBCs the #eZ80 in the Agon solves the problem of having 8-bit simplicity without a 64KB limit or painful memory banking. A native 24-bit address-space greatly simplifies OS/app development.