So this is probably not a must have. Bit it is a nice to have. I put one on my long hose reg on the twin set. It makes swapping out hoses easy as you don't have to turn the entire hose to screw it into the reg body. Install this first with a hex key and then turn the inline swivel when installing the hose instead of a 7 foot hose. It allows the hose to rotate freely on its axis so it is less likely to kink or get a case of the loops. The long hose always comes out straight when you donate your primary. No loop dee loops . (For lack of a technical term). Quality is good. No leaks. Some may argue that an addition like this (as well as other swivels, quick connects etc.) is / are an additional, potential point of failure and should be avoided. Up to you do decide where you come down in that debate. I've had no issues. Dive safe everyone.