I dont need prepared stats to know what i have seen. More penalties have been missed/saved because of using that nonsense stutter bullshit than when a player just picks a spot and smashes it. Most of the time (but not ALL the time), if they miss because of smashing it, they blaze it over (and this is mostly done by defenders, it feels like). We've seen penalty shootout saves/misses because of the stutter, we've seen penalties in regular time saved/missed because of the stutter. Hell, even Kane missed a pen while stuttering and luckily got to retake it and then smashed it in the goal without the stutter the second time. Mbappe missed with a stutter. Messi missed with a stutter. Bruno G missed with a stutter.
Edit - apparently they did prepare stats for the stutter conversion rate v non-stutter
43% of the stutter pens have been missed. 32% of the non-stutter pens have been missed. This does NOT include penalty shootouts.