They're insecure [1] and far from usable.

[1] https://madaidans-insecurities.github.io/linux-phones.html

Only if your threat model is equal to the one from the GrapheneOS crowd, and only if you value freedom less than maximal security. It's fine if this is your choice, just don't say this is the only reasonable choice.

Concerning "usable", Librem 5 is my daily driver. I have no backup phone.

Also, after skimming your link and seeing "Hardware kill switches are nothing but marketing frills", I can state that this is nothing else than FUD. Kill switches can protect me, when GrapheneOS can't. You have to trust that your proprietary modem never spies on you. I don't have to. Also, here is a couple of nice discussions of this article: https://news.ycombinator.com/item?id=37507414 and https://news.ycombinator.com/item?id=28500824