I got mine today as well. And it's true, nothing fits except the included switches.
It is actually reasonably well built and doesn't feel shoddy. The included blue switches feel just as good as MX Blue IMO, if there is any major difference it's probably very small.
The spacebar stab was broken out of the box however, so this is a good enough excuse to return the keyboard.
The Team Wolf modular keyboard is probably a much better option, especially if you want to use Gateron or Zealios, both of which I think have the proper LED cutout in them. Also waiting for Glorious to release their TKL but their full sized modular board is also quite good though its the most expensive.