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Not exactly cheaper to get than a Jonsbo case.

If you go look for a used regular PC case, older model will typically have more 3.5" bays. By older, I mean +15yo.

If you have access to a 3D printer, you have options to make more drive bays on the cheap.

You will have to go for a modern power-supply still, in order to have enough SATA power plugs.

They already brought webserial.

They are talking about the firmware that runs on the device. The user front-end to easily configure it is another story. Hopefully it’s going to quickly get support for Linux as they are starting from well established Open-source projects for keyboard firmware (QMK and ZMK). If it works like for keyboards, you will be able to configure your mouse with something like VIA that runs on Chrome/Chromium (and maybe one day Firefox ?) using the WebUSB API.

I have 2 keychon keyboards, an old one and a newer one with QMK firmware. Both have worked perfectly well for Linux. The QMK one is easy to configure with VIA once the device permissions are sorted out.