Sounds exciting but a little scary. Have you used it?

I have used it in order to develop an eclipse plugin for vim. It took some time to set up, but then it worked as advertised. I could use vim inside eclipse. It exposes all the mistake detection and completion stuff of the regular Eclipse editor, but triggered by keybindings instead of automatically.

Not exactly. I tried setting up a really complicated system with Eclipse running as a server in a VM and my local Vim serving as the head to it, but haven't gotten that working yet.

I prefer Vim as the frontend, but was hoping to add Eclipse's code correction and refactoring to it. But that's also the most complicated of the three options, and least well supported right now.