Can't speak specifically to these cleats, but I can tell you that SP_son (LHP/1B) has worn mid-height cleats for years (since 12U/13U days). He has never mentioned any mobility concerns with them, and has had more than one hard comebacker catch him on the extra padding at the ankle. Rather than a bone bruise (or worse) he's just had a little more motivation to pick the kid at 1st.
I'm a believer in the extra ankle support and protection if the player can overcome the fashion statement aspect of playing in higher cleats.
For what it's worth ...