Now that might be a bit unusual choice of lens, but news photographers around the world rely on their zoom lenses that won’t open up more than f2.8.
And for a prime lens in this long focal length, f2.5 is still quite okay, Canon’s EF135mm opens up until 2 that’s only 2/3rd of a stop faster.
Really fast lenses get attention because they are the most expensive, and shallow depth-of-field has been in fashion… I think in part because it gave photographers a way to distinguish themselves from smartphone wielding amateurs. I predict this is on the way out now that portrait mode fakes this look! But a super fast lens is in no way necessary for taking great pictures.
I’m sure there’s plenty of valid criticisms for this project but this one does not convince me :) Personally I wonder more from an ecological point of view, i.e. why use all these resources when there’s plenty of unused lenses on the second hand market. But then again the Open Source aspect is commendable.