All keyboards are “mechanical” in some sense, or at least most of them, in that something moves. But what we call a “mechanical keyboard” is one that has individual switches under each key cap, instead of some sort of silly squishy membrane. This gives the keys a different tactile sense, and often, a sound.
This post — Mechanical Keyboards What Are They And Which One Do You Want — is a little, but not too much, out of date. The basic information is correct. There are one or two more kinds of keys than described, and there are emerging manufacturers that may or may not be making good switches, and there are many more offerings of el-cheapo keyboards. And, still, the DasKeyboard is still one of the better (and more expensive) options.
My Avant Stellar keyboard finally broke in enough places (I’m tough on keyboards) to require major repair or replacement. I looked briefly at really old Northgates (20-30 years old?) on ebay, bid on a few, but was outbid and decided not to spend an exorbitant amount of money on a decades old untested machine. I also realized that I have two computers sitting next to each other, and when I change between them, it feels wrong, because they have two entirely different kinds of keyboards. But, I realized, if I get a new DasKeyboard for my Linux machine, since I have a Mac DasKeyboard on the Mac, then I would quickly become accustomed to switching back and forth and all would be well. So, I got the Das Keyboard Model S Professional Cherry MX Blue 
Except possibly one thing. You may recal that I had earlier complained about the font used on the key caps on the DasKeyboards. At the time, I used stick on labels to upgrade the DasKeyboard to how I like it. For some reason, as I sit here typing on the new DasKeyboard with the small typeface that I don’t like much, I’m not bothered by it, so I may not make that change. We’ll see.
So now all is well in keyboard land, and my pile of no longer in use keyboards available for spare parts grows.
