So I've been playing around with F21U4 and it's actually a pretty good mixup tool, at least for the Dualist variation. I've caught people with bicycle kick after it, enhanced solar flare and orbs. Still need to work on incorporating it a little more effectively on where it fits in his toolset but overall it's a swaggy looking move to catch people off guard with every once in a while. F21U4 into stance change seems to be safe on block or at least hard to punish because of combination of pushback and block stun.