boomx5:Caveline only. The o-ring thing isn't taught in GUE classes.
I don't know what is current GUE curriculumn. But, the general rule is, if you absolutley don't want to lose it, cave line. So, backuplights, primary lights, stuff in your pockets, etc. are caveline.
The 7' hose and stage regs are a different animal. Something breakaway for the reasons gien above is best. I have seen both o-ring and straight tie wrap (which is less break away, but still easier than line) used.
For the HP gauge, it goes back and forth. Since there is no way to lose it, a breakaway makes sense in case it gets hung up. However, the o-rings do tend to get old and break rather often which is a pain and is the reason many people go with cave line here too.