girth work

I am attempting to understand the science behind sleeves and how they are used to cement gains. Can some tell me that if they are literally squeezing the penis (kinda) how do they cement girth gains if they do at all. I can see how they would cement length gains but if wearing tight underwear...

So I'm trying to figure out what pump I should get. I've used bathmate and had decent success with it, but on my last post the mityvac was recommended to me. Anyone who's tried both wanna share their opinions?

Question: - What is the best program/routine for girth work?