I'm unsure of the specific type of Marquardt switch as it doesn't match up with any of the three on the wiki but it is a fairly smooth switch, more so than Cherry Red or Black in my opinion.
The caps do fit MX switches and vice versa. They appear to be dye sub caps, I believe ABS but I haven't confirmed yet.
Closed off nice and pretty:

Opened up:

Oh look, switches!

A single switch showing the logo.

But...will MX caps fit? Of course.

Will the caps fit a MX Switch? Sure.

Is that a LED switch for capslock? Nope.

And the cap for capslock.

The keyboard itself.

Back showing PCB.

Main PCB (Motherboard?) of everything.

And it does work after a bit of oiling the rails.

I'll take more pictures this weekend as I'll have a Canon 650D over my 300D meaning none of that ISO 400 noise. In the mean time anyone know what switch this is specifically?