I have 5 M&P's. Four FS with out thumb safeties. Did have my doubts with the first one (that didn't last long), zero second thoughts on the next three FS. NO thumb safeties.
I DO like the thumb safety on the 9 Shield. It's a no use if holstered and a positive on if stuffed in a pocket or purse. It's a no brainer on why they put it on the Shield.