yes I have. The x curve fit me ok, not great. I used it for a season and it was alright. The Krux was obviously superior in fit when I made the switch though.
According to Stone Glacier, something like 80-90% of the guys they fit in their showroom fit better into and vastly prefer the Krux. The X Curve only fits your back if you have a specific curvature.
Rule of thumb, direct from SG: stand with your feet together against the wall. Put your heels, butt, and shoulder blades against the wall. Take your hand, make a fist, and if you can fit it easily between the wall and the small of your back, the x curve is what you want. If your fist doesn’t fit without pushing ANY part of you away from the wall, you want the Krux.