My Sidemount regs are Apeks TEC3. I find that because they come in right and left version, they fit just right with left and right valve of the cylinders. Nothing is protruding.
As for the routing of the hoses, everithing is more cleanly routed and in the same direction. my gauges are hidden from the way, not lolipopped in front or shoveling silt, but easily accessible.
My left second stage reg (XTX50) has a 90 degre elbow and the gas is coming from the left, so there is no hose going behind my neck. That reg is on a bungee necklace. the hose is 22'' long, just enough to go from the tank to my mouth.
on the right side is the long hose wraped on the tank. again, no hose behind my neck.
as I said, the neat thing is having a right and left reg to fit with a right and left valve and having nothing protruding.