I tried the imthere back rest also. I think I'm going to do the same thing just using two sit drags. One high one low. I could sleep in it also. I'm a big guy and I'mthere and g2 saw me flat against the tree feet dangling and upside down in my sitdrag without a belt and it didn't move. It took the assistance of my feet walking up the tree to get upside down but it still didn't slide. I am adding a riggers belt to mine just as a redundant backup tied into my tether. I also am going to use the sitdrag as a linesmans belt once I have the belt sewn in.
If you would feel more comfortable with leg loops or shoulder straps by all means add them. I can just say that I can't fall out of mine. Without a belt it can fall off if you when unweighted. The only reason I am using a riggers belt is in case for some reason I fell a few feet and the loops on the sit drag broke. The only way I could imagine that happening is if I used my tether while climbing lone wolf sticks and climbed up a stick length without moving it up. The only way I see that happening is If I lost my linesmans rope. The only other time I might have slack in my tether would be standing on the platform to turn around and shoot behind me. Shouldn't be more than six inches of slack but there would be some. I'm not saying the loops are a weak point but I don't know they have been tested with a dynamic load since they were made for ground use.
If you would feel more comfortable with leg loops or shoulder straps by all means add them. I can just say that I can't fall out of mine. Without a belt it can fall off if you when unweighted. The only reason I am using a riggers belt is in case for some reason I fell a few feet and the loops on the sit drag broke. The only way I could imagine that happening is if I used my tether while climbing lone wolf sticks and climbed up a stick length without moving it up. The only way I see that happening is If I lost my linesmans rope. The only other time I might have slack in my tether would be standing on the platform to turn around and shoot behind me. Shouldn't be more than six inches of slack but there would be some. I'm not saying the loops are a weak point but I don't know they have been tested with a dynamic load since they were made for ground use.