One benefit of a stand up desk, from my experience, is that it helps battle grogginess. Since I started using a stand up desk, I have rarely had any mid afternoon, post-lunch fatigue.

I tried a stand up desk for a while before putting together a treadmill desk. I found with the stand up, my legs and feet got tired quickly while standing and I was too easily distracted by shiny things. The treadmill is a bit more captivating and that helps my mental focus. And my feet don't get tired for hours.

I am looking into getting one of these. Do you have any recommendations?

I made my own ( http://imgur.com/a/BczGu#26 ) and it's great to work at. If you're buying one, I'd recommend picking a good desk without the motorized bits. Instead of getting something that goes up and down (so you can sit at a normal chair when you don't want to stand), get a tall stool for when you want to sit.