Great choice. I've had my Shield 9 for about a year. I never carry it with the safety on. I keep it in a Kydex holster, and the safety is completely covered by the holster, so there's virtually no chance that it'll engage itself. I still thumb sweep by habit (1911 shooter), but the safety's already off.
Great..what made you choose this over the Glock 43? Just curios
This is what I personally like about the Shield vs. the 43:
(1) It has a safety. With a safety like the Shield's (flush and flat), I don't carry it with the safety on, but I do like having the safety for when handling the gun at home. I like that the safety doesn't prevent the slide from cycling, so I do safety the gun when unloading or loading it at home. I also keep the safety engaged at home, whether it's unloaded or stored loaded in the safe.
(2) I prefer Smith's Melonite finish to the slightly rougher finish on the Glock.
(3) I prefer the stainless steel slide/barrel of the Smith to Glock's steel.
(4) I prefer the more upright grip angle of the Smith to the Glock (see above -- 1911 shooter here).
(5) Capacity. (In stock form -- I'm not into modifying carry guns, so I don't consider any aftermarket parts there.)
(6) Price. I personally believe that there is no appreciable difference in reliability between either choice, so even if everything else were equal to me (safety/no safety, ergonomics, etc), I'd have to justify to myself that the Glock is worth at least $100 more than a Shield.