I purchased a Thelio Mira awhile back and have been happier with it than any other PC/laptop I've owned before.
The big value add that System76 is having a Linux desktop that is guaranteed to just work out of the box the same way you would expect and Apple machine to work out of the box. In fact, I've probably had less issues with this machine out of the box than any new macbooks I've had in the past few years.
I've built plenty of my own PCs before and run linux as my primary desktop multiple times, and my Thelio is a wildly better experience than in the past. The build quality is excellent and for the first time I can really use Linux as my primary desktop with no problems.
Building a PC yourself is always going to be cheaper, and for many people that's the preferred path anyway. The point I'm at in my life I would much rather pay a premium to not have to worry about that at all (especially when it comes to hardware on linux).
If anyone is look for a "just works" linux PC, I've found system76 to be a great experience.