Do you think Purism will stay true to their goals, or have to compromise privacy of their customers to achieve greater success? Will it become another Walled Garden, unless it isn't already?
You can use OpenPGP with your email, Matrix to chat, Mastadon for social, and OpenVPN for tunneling without becoming dependent on Purism.
I think compromising on privacy would destroy their value proposition, and alienate all their customers. That's unlikely to happen. And similarly, I don't think it's likely they'll become a walled garden, because most people will be outside their service.
However, the basic question is: why would you want to tie your online identity to their service? Get your own domain name, and use service providers to support that. You can still have exactly the same features as Librem One without being tied to them ...
Easier said than done for some. I think that's who they're aiming for as clients.