The XLR-1 box seems overpriced, but when looking for a less expensive solution, people need to realize that
there's no such thing as a universal passive adapter from two XLR inputs to an unbalanced mini-plug unless it contains a pair of audio transformers. And the good ones of those, such as Jensen or Lundahl, are quite expensive (see for example
http://www.jensen-transformers.com/ms2xx.html).
Without transformers or active circuitry, no matter how you wire the box (among the several possibilities that exist) there will be some good mikes that it won't work with, or won't work properly. It may pass no signal at all, or it may pass signal from one output lead while it shorts the other one to ground, increasing the distortion and lowering the maximum SPL of the microphone. Or it may work fine. But that depends on exactly how the box and the output circuit of the microphones are designed. There's no one formula such as "just connect pin 3 to pin 1" or "just connect pin 2 to pin 1" or "just connect pin 2 and leave pin 3 hanging" all of which I've seen people give out as if it was the most obvious, well-known thing in the world.
Sorry to be the bearer of bad news here, but let the buyer beware. There is a standard for balanced operation of phantom-powered microphones, but no standard for unbalanced operation. If you imagine that this subject has a simple solution, you're simply wrong and you're headed straight for the problems I'm talking about.
--best regards