Most VR headsets on the market are not clear enough to display text. For example, Meta Quest Pro and Quest 2 both have pixel densities around 21 pixels per degree. While a 27" monitor running at 2560x1440 at an arm's length (40 degrees horizontal FOV) will have a pixel density of around 64 pixels per degree. 64 PPD is very legible and usable for office applications, chatting, and similar things. One can see individual pixels in very aliased and high-contrast images, but not otherwise. In contrast, 21 PPD is not great - most text will be either very blurry or aliased on an equivalent virtual display. The math is simple: 21 pixels per degree x 40 degrees (which is 1/3rd of the human eye's horizontal FOV including peripheral vision), equals a display resolution of about 840x473 at 16:9, or close to 420p. Clearly, this is not comfortable to do office work with.
SpaceTop has a relatively low FOV but much higher pixel density of about 46 pixels per degree. It's about twice as good as what Meta Quest Pro and Quest 2 can do. It also seems to have individual floating apps rather than entire screens, but if we would assume that one would like to have a typical experience roughly equivalent to a 27" 16:9 screen at an arm's length, that virtual screen would be at about 1840x1035. I think this is right at the edge of what I would consider comfortable. Most graphics, including text, would probably be slightly blurry, and anti-aliasing blur or aliasing artefacts would be clearly seen. But I would not get too frustrated by it.
That's a trend with AR glasses when compared to VR headsets - they have narrower FOV and higher pixel densities. So they are overall better for non-immersive office-like applications. Still, the holy grail of productivity AR headsets is something like 60 PPD and at least 90 degrees horizontal FOV x 60 degrees vertical FOV. At that point, I would say the differences between our actual vision and what can be shown on the glasses in terms of resolution would be not significant, assuming the eye balls always point within 30 degrees of the center of the AR display. But this means a resolution of around 5400x3600 per eye. Or approaching 12K in total for both eyes combined.
SpaceTop is probably much more usable for office work than many of the VR headsets on the market. And it seems like they're aiming for a similar experience to having one or two 1080p 27" screens about a meter away from one's face. I think it's right on the border between fun tech and practical tech. Slightly higher PPD and FOV would push it more into the territory of practical tech for me, someone who writes and codes while travelling. Now it sounds good but not revolutionary.