If I'm a linux user who uses firefox currently, what's the value prop for this browser? I already get privacy and extensions, is it just for testing my app on webkit?
You can already test a site on a webkit engine in Linux using Gnome Web (previously Epihany) or LuaKit ( https://luakit.github.io/ ). But it is always good to have options, even if commercial ones. From that aspect Orion on Linux is good news.
As I understand it, Orion was originally developed because Apple doesn't allow you to select Kagi as a search provider for Safari.
The main benefit is that Orion (contrary to Firefox) has a business model. The downside is that it's not open source. They have some explanation on why, but it might be a deal breaker for someone.