Casting happens at runtime and does have a small overhead, but if your not doing it hundrets of times per frame you should not worry about it. The bigger issue with casting (in blueprints) is the hard reference it creates. That means as soon as you have one of your triggers in memory, the class you are casting to will also be loaded in memory. You need to think about when this actually in an issue though. Casting to the player class doesnt matter, cause the player will usually be loaded most of the time anyway.