It is a practical consideration for a customer shopping for a device with an option to run a FSF-endorsed distribution other than PureOS or a customer who already purchased a Purism device with such intention in mind, which perfectly fits the situation that the topic starter found themselves in. Should the blame for such expectations be entirely on the customer? The product page for Librem 11 states as follows.
Shipping with PureBoot and PureOS, you make sure that the Librem 11 is fully yours and is respecting your Privacy, Security and Freedom by default.
However, it does not clarify that the firmware jail technology is being used for the device. This technology is not an industry standard. The prospect customers should be informed about the trade-offs that it entails. They are significant enough for me to be the only reason to not buy a Librem 11. They may or may not be significant for other customers. For comparison, I would still buy and recommend Librem 5 considering how unique it is, even though I fail to see the benefit from the firmware jail instead of a file.
Please consider the impression from the following passage, which comes from a Purism’s blog post returned by web searches for “firmware jail Librem 11” and “firmware jail Purism”.
PureBoot’s Firmware Blob Jail feature provides device firmware for operating systems that do not include any non-free components, like PureOS. Using the Linux configurable firmware search path, it does not require a special kernel or any special operating system support.
Trisquel falls into the category of “operating systems that do not include any non-free components”. I understand that @jonathon.hall did not mean that Trisquel would be able to utilize a firmware jail, but the phrasing makes it appear that there could be other operating systems besides PureOS that could fit the description, so that other FSF-endorsed free GNU/Linux distributions reasonably come to mind.
The communication from Purism on the matter is confusing and may build wrong expectations with the customers, potentially resulting in a bad image due to dissatisfied buyers and turning off some prospect customers and members of the free software community even for the products which could run Linux-libre or for the relevant free software projects.