Absolutely agree with the reviewer on the build quality of the Ricoh GXR and related modules. When assembled as a unit they feel like they are carved out of a block of solid (but light) metal. I’ve been carrying one everywhere for a  year with zero issues. Invest in a screen protector for the back though.

The more recently released A16 24-85mm Camera Unit uses a more modern Sony sensor in it.  You’ll find better high ISO performance there.

The Mount A12 module you mentioned has what is probably the same slightly older sensor in it that the 28mm unit you evaluated has. But that Mount A12 module also has other magic pixie dust which makes it truly worth looking at for M lens users. It, like the very expensive Nikon D800E, doesn’t have an anti-alias filter in front of the sensor. That and other characteristics makes the module is specifically designed to support the demanding requirements of virtually all rangefinder lenses, which include some of the best and most expensive 135 format glass in the world. But yes, the Mount A12 also could use a more modern sensor in order to access better performance at higher ISO sensitivities. 

However when used in its sweet spot, there is no other camera available for M lenses that can touch it except for buying a Leica digital M for thousands more.

The hope is that Ricoh updates the most popular lensor and Mount units in the near future but we may be waiting until Feb/March to hear anything on this. They are also digesting their acquisition of Pentax; hopefully in the new year we’ll see some fruit borne from that new tree.