I recently purchased an M&P 9 w/ thumb safety. I ordered it with an APEX sear, APEX striker block, and APEX competition striker spring, all installed by G&R Tactical. The trigger pull is super nice for striker fired Tupperware (a hair less than 4# pull weight). It's like having a slicked up Glock 19, with 1911/Hi-Power ergonomics. Actually, aside from the somewhat vague reset (I'm not stuck on the super positive Glock reset like many Glockophiles are), it totally kicks ass on a tuned Glock 19 trigger. I highly recommend. As soon as I get my holster made, my Glock 19's will be getting some time in the safe.
My reason for ordering with the thumb safety is as mentioned above - shit can happen when you're reholstering. With a lightened pull weight, a strap, twig, or whatever, somehow introduced into the trigger guard while holstering, would have a greater chance of pulling the trigger, causing you to shoot yourself in the leg. Since the thumb safety is in the same position, and same general shape, as those on my primary carry 1911, there's no awkwardness, delay, or doubt in its operation, for me. As a bonus, it keeps my right hand thumb away from the slide stop when firing, so that I won't accidentally lock the slide with rounds still in the mag, or keep it from locking when I've emptied the mag.