I don't buy this. For example, if I rent an apartment, but there is a locked cupboard in it where the landlord stores a bunch of tools and other bits and pieces

I don't buy this. For example, if I rent an apartment, but there is a locked cupboard in it where the landlord stores a bunch of tools and other bits and pieces, I don't complain to AirBnB that I didn't get the full use of the property, and start a campaign suggesting they are infringing my rights by not letting me access the landlord's cupboard? If I buy a device that is advertised to do X, and this is accomplished by running a program to do X on a locked-down general purpose computer, then it is (assuming no issues with program X) fit for purpose by any definition. If I wanted a general purpose computer, I would purchase one. The fact of the implementation detail being a general purpose computer is irrelevant, it doesn't impair my ability to do X if I cannot remove X and install Y, in fact it improves the ability to do X, by preventing the possibility of all sorts of misconfigurations and installation incompatibilities. I admit that it's hard to find real-world analogies, and the landlord-cupboard above is not a perfect fit, but I still have no problem with saving money by purchasing a device that does one thing, and one thing only. I have no expectation that it be hackable or extensible, unless it is advertised as such.