HI Paul
There is no difference between Air and Boat, air range is out of sight a good mile or so, boat range (not submarine) is at least 1/2 mile with a well mounted antenna.
Mode 1 and 2 are right hand stick trottle and left stick respectivley, most tranies allow throttle change over, its just a small ratchet moved from one stick to the other.
Dont worry about interferance, thats the point with 2.4ghz, they hop frequencies and avoid each other, not like 27, 35, or 40mhz, held to the same channel by crystal control. At my club we can have 20 - 30 members sailing with no problem.
Your Saturn 4 is similar to my Radio Link. Lot of our guys have them, no problem with interferance, would say that the more expencive sets are more advanced that the simple sets, some onlt hop over 2 frequencies, Futaba etc hop over dozens, but this is done in micro seconds.
Mark