First off, note that Behavior Trees only dictate what to do, not how or why to do it. How and why are still defined in Blueprints. (And probably C++ though I haven’t seen how to do that yet)
I haven’t instrumented performance impact on either, so I can’t weight in on that. But in games don’t listen to any performance claims without actual hard data, people love gut instincts. In fact you should use the tool that makes you most productive until you actually find a bottleneck.
Personally I would not want to implement a behavior tree like this in blueprints. (Note that this is only a section of an AI’s behavior from this game. Click the image for a link describing the logic behind using Behavior Trees.