$139 (early Kickstarter price) feels surprisingly low if it works like they claim - a wacom with a display is significantly more expensive, lower display resolution, less portable, and totally different ergonomics (for good or bad). Though they are also a second screen.
Makes me wonder if it'll work on other computers. Not as slickly of course, but it'd probably still function, except maybe for the software (if any)...
You won't get any of the subtle display animations and UI niceties for a capacitive touchscreen on desktop. It will function like those old Nokia touchscreens/Windows Mobile stylus point and click.
Wacom is a big name brand. You can get pen displays from brands like XP Pen and Huion for not much more (https://www.amazon.com/XP-PEN-Artist12-Battery-Free-Multi-Fu...). And they are true second displays. If all you want is a pen tablet then those are much less expensive.