How does the LEGO Technic 8879 controller work? When you make it go forwards/backwards and let go does it stay at that speed like the more recent helicopters or does it go back around? And how does it go forwards and backwards, is it like the 8885 controller where you have to have a motor for each of the front wheels to turn?
It is not spring loaded, meaning if you set a dial to a specific value it will stay there. There are two channels that can be controlled with the two dials, and either can be set in one direction ("forward") or the other ("reverse"). I put these terms in quotes because their exact function depends on your model, but in the simplest scenarios (like controlling two separate train engines) they act so.
A single channel (dial) can control one or more motors, but in the latter case all motors will receive the same signal which means they will rotate in the same direction with the same percentage of their maximum speed - different motors can have different maximum speeds.