I'll compare the unit to the Scarlett 2i2 3rd Gen that I've been using for years and was interested to replace with the Vocaster One, especially given its currently discounted price point (<50€). My main use cases is video conferencing, which seems to be closer to the advertised focus of the Vocaster line than the Scarlett line.
Build quality and basic functionality are great. It's a solid device. I basically got it working by plug & play alone, even on Linux. The physical buttons are well designed. I also liked having the XLR input on the back of the device, which allows me to hide one more cable on the desk. I've missed a mute on the Scarlett 2i2, so that one's nice to have.
For firmware updates and software-only settings, I need to connect to a Windows PC or Mac. That's disappointing, but as advertised.
The size of the device is puzzlingly large for the controls it has, but then again it handles well; all user-facing controls are big and clearly separate from each other. I can see operating it while recording yourself, more so than with the Scarlett.
My colleagues reported lower gain than they've become used to from my setup, and lower quality after I increased gain further. I did not spend much time optimizing the setup for reasons to follow, so take that with a grain of salt.
On the other hand, much to my annoyance, some features can not be controlled without their companion software (e.g. switching enhance modes, or muting individual inputs), 3rd-party software (e.g. _not_ mixing computer sound into the microphone audio), or not at all (turning off direct monitor; different gain for headphones and speakers).
Unfortunately, these limitations are deal-breakers for my use case.
Compared to the 2i2 that I have (which has a similar MSRP and _smaller_ physical size), the Vocaster One seems to provide little flexibility. If you do not want to use it solely for its poster use-case -- recording yourself for podcasts or videos -- you should probably stay away. For video conferencing, at least, the device is not suitable, at all.