kenn1320 has it right. You don't need to buy anything fancy. You are not taking a dynamic fall on a linemans belt, so you don't need the 22kn rated stuff. I wouldn't worry about side loading the carabiner either. Here is a shot of just using a carabiner and prussic loop. You could leave one end free in the prussic as I show or you can run a full loop. Point is that if you should slip off your stick, the monkey tail will catch the tree more reliably than just the belt.
Here is a video of an electric lineman falling to the ground when his belt didn't catch (skip to minute 2:33).
View attachment 7881
My prussic loop is just 5/16" plain double braided dock line, not any of the fancy tech cord. It splices easily for a neat package.