I am still typing on my Filco MJ2, which was my first mech.
But I was never fully satisfied with it.
First, as others have noted, it is noisy. Noisier than comparable keyboards. [MX Brown].
There is a little ping in the case, but mostly rattle from the stabs, and the switches themselves.
The stabs are a main culprit here. The Costar stabs don't play well with a lot of aftermarket modifiers. And I haven't lubed them.
Lubing them is a priority this summer.
But, man, it sounds almost like a machine gun.
The Filco feels solid because it has a double-thick plastic case, which gives the impression of quality. It's certainly sturdy, and I appreciate that.
But the board lacks subtlety. It's got thick plastic and a double-sided PCB (which I can't see), but the stabs rattle and the keys bottom-out hard. And I get the sense that MX Browns weren't designed to be mounted on such a rigid, metal plate.
My Varmilo came quieter out-of-the-box, and felt like a more professional typing experience.
And I have a Leopold FC900 PD on the way, to directly compare to the Filco.