Just FYI, none of the things from the ledge are "guaranteed" when you grab it in the Demo so far. However there are guaranteed options if you know what your opponent will do -- Mario, for example, can ledge steal from Megaman and get a guaranteed u-air if Megaman holds towards the stage and jumps. If Mario wants to hit with this he HAS to immediately jump off the ledge and u-air, otherwise he gets footstooled by Megaman.
From what I've seen, it's just a mixup game. Have the player who grabs the ledge just spam air dodge and try to punish it by dropping off the ledge and attacking the moment you steal it from them. Their air dodge will come out first. This indicates that they get to move first.
If you can call your opponent's option, you get a free hit. If you can't, you won't. There might be a few characters in the full game with larger hitboxes that can do more, but so far I have yet to see it.
Also don't call it vexxing, it makes you sound like a tool. It's just good ol' fashioned edgeguarding, taking the ledge is nothing new.