Open C#plus any of the octave keys was problematic for me because of the forward pressure of the left thumb with no front keys down for support. I put in some batteries for added counter-weight which helped a little, but I was still spending an inordinate amount of time practicing octave-crossing patterns that involved C#. I also needed a lot of extra lip pressure just to stabilize the instrument during these patterns. But then I discovered that the four-point harness I use for bari sax really helped stabilize the WX-5 because the lower straps provide counter-force against the left thumb pressure that tends to push the WX-5 away from the body. It worked for me, anyway!