That's a really clever design.
I wanted to take a look yesterday, but wasn't allowed

Thought you used monkeyfarms design but this is a better solution for Enderman it looks like. Wonder that you do not get the Monster stuck in in Piston glitch. I've given up on the piston design and went back to water channels or falling holes which does not work well since the monster stopped moving when you are to far away.
I would love to be allowed into your spawner. Some enchantments come in handy for my project