Concerning the old hardware, it's the most powerful phone which can run latest Linux kernel and the only one recommended by the FSF [3]. Specs is not the whole story in smartphones [4].
[0] https://source.puri.sm/Librem5/community-wiki/-/wikis/Cellul...
[1] https://puri.sm/posts/librem-5-4500mah-battery-upgrade/
[2] https://source.puri.sm/Librem5/community-wiki/-/wikis/Freque...
[3] https://www.fsf.org/givingguide/v11
[4] https://source.puri.sm/Librem5/community-wiki/-/wikis/Freque...
https://www.techrepublic.com/article/librem-5-review-the-lin...
https://forums.puri.sm/t/received-my-librem-5-evergreen/1087...
https://www.reddit.com/r/Purism/comments/jzj6s1/i_have_recei...
You own it. You control it. YOU have the power. That's the damn point.
> Is their hardware really open source?
The phone is going to get Respects Your Freedom certification by the FSF.