I have the 2018 ION CS Wave Harness, this was bought to replace a Ride Engine harness which I had certain build quality faults ( the shell cracked at the webbing attachment points, it wasn't the carbon version), The Ride Engine harness was, for me, very comfortable and didn't move.
The ION Wave is slightly softer in flex, and slightly more plush in back padding, I preferred the more engineered hard feel of the RE.
The build quality of the ION is excellent, and shows little sign of wear after one years use. it is comfortable and doesn't move.
I have modified the ION, the spreader bar is very padded, and seems bulky, I removed the rubber pad at the back of the spreader, this brings the sliding rope closer to your body (less leverage) and gives a more locked in feel.
The harnesses weight about the same.
Final point , the sliding spreader bar does not have the "over-centre" locking system, but a more usual "bar and hook" system.
Prefer the ION.