I've used the Vega which is a pretty minimal seat harness. I used that with the ill fated first generation Dakine rope slider bar which would come unhooked all the time.
The vega would also ride up into my crotch with the leg straps at times, something the fusion doesn't do as I assume the power belt holds it in place better.
Also the vega doesn't have much if any padding in the hips which for a really long session can start to be sore for me.
So I went back to the fusion in 2018 . In part because it was less bulky. I know some of the die hard fusion fans didn't like the design.
It looks like the reflex is like the vega without the power belt and withou the webbing you can run to hold the hook down.
So I don't think that is what I am looking for but thanks for the suggestion.