I don't know much about the Icon (in the water wise). But the Galileo gives you Remaining Bottom Time rather then Air time....the difference is the RBT takes into account EVERYTHING that's going on. Remaining Air, Depth, NDL, Breathing Rate, Temp, Safety Stops, Everything, and that translates into an accurate Time frame for how long you can be at that depth. As oppose to Air Time, which is just Tank Pressure and NDL's. Among other things, UWATEC has been doing this for almost 50 years. I don't really know what Mares experience is (or who's building it for them).
Also there are a few minor differences between the Sol and Luna. Sol has the Heart Rate Monitor, can switch between 3 gases, and/or can give you readings of 2 other tank sensors (like you wife and kids). While the Luna, 1 gas, 1 sensor and no Heart Rate. Personally I prefer the Luna, it's just me, I'm just doing easy non tec dives, and I like the Black face too.
Hope this helped.