It's made by people who care about software freedom. It doesn't use the common ARM-based SoCs which require proprietary drivers and will be unusable with modern software in a few years. Everything except the cell modem (on a replaceable M.2 card connected over USB) runs 100% free software. The device as a whole runs Linux with Gnome, and Plasma Mobile + others also developing for it. The company contributes back to the OSS software they use/improve.
It doesn't have the form factor of the TRS-80 Model 100, but basically the deal you get with it is that you pay the price of a decently high end smartphone in exchange for a midrange smartphone which is completely controllable by you, as much as a normal Linux desktop, but still offers a 'pretty good' UI out of the box for normal phone usage.