A number of people have requested more information on how the capo system works, so let me explain a bit for those technically minded folks. Each fret (or as many as you wish) has its own integrated capo that can be either in the up or down position. The capo itself is a piece of 1/8″ steel with a very fine slot cut into it to accommodate the string. This steel is housed in a brass sheath to allow easy up and down travel without wearing the wood. Underneath the capo steel is a small neodymium (rare earth) magnet, just strong enough to hold down the capo and keep it from vibrating when not in use. When you want to engage one capo, there is a stronger magnet that is supplied (which conveniently stores at the base of the neck via its attraction to the interior magnets). Holding that magnet on any capo will pull it up just high enough to allow insertion of the string. The slot will always be at the right height thanks to a stop on the underside of the capo that will only allow it to go up so high, and can never fall out.
Is there ever any problem with the string coming out with heavy playing? To avoid this happening, I suggest simply using two capos. Generally I have the 2nd fret capo also in the up position with the string behind it, not in the slot. This puts side pressure on the string, which makes it very difficult to come out of the functioning capo during even very heavy playing. If you will be capoing either the first or second fret, there is no need for an additional capo as the capo is close enough to the nut that the string will not want to come out.
Can you tune the string while it is capoed? Yes. The string still tunes quite smoothly, and without string breakage. Furthermore, using the capo does not throw the string out of tune when changing to another capo or playing without it any more than pressure from your fingers does while playing.