the ob, I installed one on mine before I attached the first atty/carto. Darwin's connector is brass, I did not want to ever be able to cross-thread it. I considered using
Loctite to keep it in there. There are differing strengths of Loctite, all are removable, but some take an application of heat that could be bad for the insides of Darwin.
A 510-510 extender is a good thing, it lets me use several different heating devices, and still let it fold. It lets me use some tanks (that won't fold) that would be hard to use, otherwise.
I think it's great that it is being included as standard equipment, but I myself would like the ability to change it. I carry mine in differing pockets, and if I sat down on it just wrong in a snug Levi hip pocket, it is possible I could damage it.