Comparing without running them side by side is hard
The 100 will appear roughly 1 f-stop faster, so at the same camera settings, so exposures about half the time of the 120.
The flip side is, that for the extra time, the 120 is going to give you more zoom from the focal length.
I'd be sceptical about those reducers...the included flattener sets the bar pretty high, and again it depends on the camera you will use. Starizona specifies an imaging circle of 30mm, which is far from the native, and I'd be concerned how my stars are going to look in even an APS-C sized sensor like that. It's a case of buyer beware...unless you track down some info that demonstrates how well it works...in which case post here
The mono (and cooled) camera really brings the noise under control, and you a calibrate with darks. It really would get the best of either scope.