One of the challenges is that most of these upgrades go through multiple production periods. Someone announces they will build a batch if there is sufficient interest, orders come in, a certain number are made and then they are out of production until another batch is announced, sometimes years later by an entirely different person.
This is what makes understanding what is available so difficult for newbies.
Exactly! And frankly why something like the U1MB is now so commonly-recommended for "serious" hobbyists who want to use their machines for a variety of general purposes - being commercially-produced for a number of years now, it's readily available, the firmware is still have active bug-fixes and maintenance (thanks, Jon!) and all the quirks associated with it are pretty well-understood at this point.