Colleagues borrow them all the time when they need a SD card or MicroSD card reader. Is it as pretty as a dedicated reader for those cards? No, but it does the job.
Saying they're proprietary is misleading a bit. The form factor makes it awkward to use elsewhere but they work just fine anywhere you plug them into.
You can likewise put 26" rims on a Ford Fiesta but it will look and function equally poorly.
My Framework ethernet dongle works perfectly fine with a Mac that I use for work, for instance.
It is mechanically disagreeable.
The weight/shape of the module will break the USB-C port in short order because it is solely supported by the connector.
For instance, by bumping the spatula hanging off your Mac.
For that matter, USB-C are crap connectors, I don't care how many graphs and BS data you show me stating they're the most reliable connector ever. I do not believe it.
They're the only types of connectors I've seen damaged repeatedly, and the only one with which I've personally experienced damage, and I've been using laptops since before many of you were born.
Sure. But this does not make them proprietary, they work fine with non-Framework laptops as well.
Can you slide them into a just-sized mechanical receptacle on a MacBook? On a Dell, HP, etc.
No.
No one wants to address the elephant in the room: it's a crap design for proprietary modules. Sure the design is open, can you use them anywhere else? Nope.
You're paying a premium for USB-C dongles that can't be used on any other brand of laptop. Apple is probably upset they didn't think of it first.