Novacustom... Never heard of it. The almost insignificant disadvantage I can see so far for Framework is that they don't use open-source boot.
Everyone so far stand behind Framework. How would you sell me on System76 or Novacustom?
Framework tried Coreboot, has problems and gave up. When buying a Laptop with coreboot you support open Firmware Development for all CPUs, many board generations etc.
Just look at 3mdeb's Dasharo guide. Its nearly as secure as Heads, on a modern Laptop!
Not true, firstly 'framework' never tried Coreboot they have provided boards to coreboot devs however, who've had issues including accidentally bricking the board. New boards have been shipped, and the origional fixed. They haven't given up though completely and the work is still being done. There was a recent talk that had to be canceled due to the speaker getting sick on this subject. Work is likely still being done, but is slow, and will continue to be so.
Still though, there's no evidence that framework has ever had or ever will have the intention of including core-boot by default. They're simply supporting coreboot devs to make it compatable
The reasoning for why the others have it is likely due to system76 and nova customs using mostly generic parts like the shell and motherboard along with being around longer. It's great to support a company that's ensuring coreboot works on their system however and pushing towards a non-proprietary future