I pulled the trigger, and I'll be sure to blog about it once I've used it for a while. I will admit I was a little worried how choppy the demo video of the dev-kit looks[1], but we'll see how it works once I get it.
I'm a little bit worried that their "Chatty" messaging app[2] (which is what the default Matrix client will be) is based on libpurple -- which is a library that has a pretty gnarly history of security issues[3]. It is using a plugin that the Matrix developers wrote[4], which I trust more -- but I'm still queasy about it.
I'm currently working on a Matrix-Signal bridge so I can continue using Signal once I switch to it (it won't have a native Signal app out-of-the-gate and I don't really want to run an Android emulator).
[1]: https://puri.sm/posts/massive-progress-exact-cpu-selected-mi...
[2]: https://source.puri.sm/Librem5/chatty
[3]: https://motherboard.vice.com/en_us/article/qkve5v/secure-mes...
[4]: https://github.com/matrix-org/purple-matrix