I think I may have got lucky with my first shin guard purchase. These are pretty awesome and saved my right leg on the first day out, but I think this was likely a product of feeling more confident because of the added protection. They soaked up the impact well and didn't carve too much damage into the guards themselves. My shin didn't even really feel the impact.
The guards do not move when riding, thanks to the cross over straps. They are well ventilated in the front (and back, but that's a given as there's almost nothing there.)
The previous review said no Velcro, I know previous/other models come with clips but these have Velcro fasteners, which IMHO is way better. Hit a plastic clip on a rock and you've got loose shin guards, Velcro just can be re-strapped.