The manual safety on the SR9 is primarily a "rule beater" since some states require one on any handgun. From a true safety standpoint, it's redundent since the inner lever in the trigger is, in effect, a "manual safety" as is the striker block. So, even if you carry with the safety off, the SR9 is just as safe as a Glock, S&W M&P, Kahr or many other guns with no external safety lever.
That said, it is an additional safety feature and, with practice, is easy to learn to wipe-off as the gun is drawn. It also makes the gun a bit proprietary since many children and adults won't know how to disengage it and can't accidentially fire the gun just by pulling the trigger.
Me? I carry with the chamber loaded and the manual safety on. Belt and suspenders.