Slowly rowlin(maxx build)

What exactly does UE stand for? I hear it alot but still dont know what it is. Also HB lol. I don't know what either of them are or I just can't think of it. Do you have a link? I wish that I could get a single speed. I think that I will be getting my rpm a-arms, carriers and my revo axles for all fours. I need to get a diff because that spool just trashes em'. So do you guys think that the feigao 540c 9xl, quarks 125b, and 6s lipos will work and be a good setup?