I have seen some major epics with people trying to get their dynafit bindings engaged on steep ice. They did not have a ton of experience with them, so maybe this is an aquired skill. This was after the binding released while traversing the ice.
Step-in AT bindings (fritschis, etc) in general can be tough to get into on really steep icy slopes, unless you can dig in just a bit so you can smash your feet into them. You can just place your feet in fritschis, but you have to muscle the heel lever to lock them in. I see this as a big advantage of tele bindings, or silvretta 500s (though I would not think 500s very good for what you are doing, who knows?)