⇒ Does it replace skins?
Nooooooo! At least, not entirely. It is not meant to replace anything, not wax, not fish scales, not inset skins. Think of it as crampons that you can put on and take off without stopping. It is a new paradigm for uphill skiing. It can replace much of the functionality of all other traction systems, but they can all be added to improve the skiing experience. It is possible to ski happily much of the time with no other traction system but it is not necessary to abandon them. For the NNN-BC system (see page) the best approach seems to be to use the claws together with a base with fish scales. And as for skins, they will be useful when the snow lacks sufficient cohesion to hold a claw. But when the snow is old or a little packed and it can hold a claw, you can ditch the skins.
⇒ Will it engage at the wrong time and cause trouble?
Highly unlikely. In normal use, gravity, friction, and inertia keep the platform fully forward and the claws disengaged. But if one is skiing backwards or doing tricks off jumps it would be possible. Realistically, for most people cross-country type skiing never involves those things.