I see this slightly differently. Before, if I wanted to be able to do something like flash firmware onto some device I would have to download some random C++ application and install and run it on my local machine. As well as having access to all of my USB devices, it also had access to everything else on my system's user context. I didn't have a way of running that code and only giving it access to a single USB device and nothing else. Now, I can avoid installing anything at all. I visit the project page and opt-in to some flashing flow that's running in a sandboxed env. When the app requests it, the browser asks me for permission and I get to choose exactly which USB device I want to give it access too. That's picking exactly the minimum "outside" access I want to give it, nothing more. It doesnt get to read/write other USB devices I didnt choose. I doesnt get to read/write to my filesystem. It doesnt get to call system APIs. It doesnt get to set itself to start at startup. It doesnt get to install an auto-updater. For me, this is a better security posture than installing random win32 apps.
Flashing was already solved by UF2, where the device-to-flash temporarily pretends to be a USB storage device. Giving raw USB access to to random websites for that is massively overkill.
I could understand it if you were trying to do realtime configuration of or interaction with some device like a printer or a Stream Deck, but something as trivial as firmware flashing?
ok, let me expand on why I don't like it...
It's making a niche rarely done use case safer at the cost of making the common case (browsing the web) less safe.
And yes, I am fully aware that I can not press the button that give random sites access... But the issue is it increases the attack surface and is yet another thing that I could get tricked by on a bad day.
The OS should really be able to run code like a firmware flash utility in a sandbox that only has access to one USB device... But instead of improving the OS we keep adding features to the browser which increases the attack surface.
I have a very long list of things I am unhappy about the OS allowing just any app to do, especially app installers/uninstallers should not be a thing.