I don't have personal experience, but they are a worthy competitor to the BOX series of clickies.
They use a different mechanism, borrowed from a kind of ALPS/MX hybrid switch. It generates a different kind of tactility than Cherry MX.
Definitely a *big click* switch, it's apparently VERY tactile. The sound can be enhanced by putting it in a big empty resonant case like the un-foamed NCR-80. Some good NCR-80 builds with Clickiez, should check them out.
The 40 G version is more reasonable than the 75 G one, I understand. You can convert all of them to tactiles, which are also pretty extreme. [If you're going that route, maybe wait for a dedicated tactile from the Clickiez line. I hear they're designing one approximating Brown ALPS.]