I bought these when my ions broke down. I was very hesitant to spend 550 dollars on a pair of boots. It has been completely worth it.
The flex of these is about the same as the ions. If you like the ions then you'll love these. The detached ankle cuff thing really helps with articulation.
Even when riding my Jones Flagship I find these boots are plenty stiff on steep technical lines. However, this is very subjective.
Basically. These are the Ions brought to the next level.
Ohh another thing.
The Ions in the last couple years had really soft toe boxes that would crumple / pinch when you used non-burton cap straps.
The SLX do not have that problem.
If these hold up as well as my Ions I may end up buying another pair in 100 days or so.