It doesn't have settings that require reflashing.
It doesn't have any trouble with "non-US backslash/pipe" key. Or hash/tilda of the same origin.
It doesn't have thresholds that drift.
It doesn't have any trouble with BIOS or UEFI, on windows or mac. Nor with anything else that knows what an USB keyboard is.
It doesn't have tap dance macros - and will never will, I give you my word.
It doesn't have NKRO - only 62 keys at once. Be careful testing that - 62 standard 65-gram keys is four kilograms of force, never mind the strain on your tendons.
As you can see - no fun at all.
It doesn't come pre-packaged either - you'll need to roll your own. So, you'll need $15-ish, some wires, a soldering iron, curiosity (as in "being curious about how things work"), and, for a couple hours, a windows machine (VM's fine).
Oh, and one last thing. You probably guessed it by now.
It doesn't have warranty of any kind, expressed or implied. You might be lucky enough to burn down whole city with it. That's not my fault.
It reads capacitive, inductive and ohmic switches (no deghosting), and probably SD microswitch by now.
The Repo's README.md contains bootstrapping instructions. this topic has a guide with pictures for the illiterate (which is another bootstrapping problem, not covered here).
FlightController (the controllers' controller), precompiled: Windows and OS X. Linux users need to compile (but at least ubuntu has all dependencies pre-built. OSS has it's benefits, too).
Hardware used is CY8CKIT-059 prototyping kit. Since the kit is $10 - there's no GB for building the controller. It's hard to beat $10 price. If, however, project MF is revived or Ellipse will decide to switch controller to CommonSense - there will be custom hardware, too.
Theory of operation:
If you want to make you want to claw your eyes out know more about capacitors, read it there, in all it's Comic Sans glory. There probably other guides, but it's hard to find one that explains energy storage. It even has pictures - but I have something better. Pr0n.