I have to agree with a few choice things that have already been said--
I think that they are more likely to prevent intended fire unintentionally than to save you from an ND you didn't intend.
I also believe that the XD's design is better in use than the 1911, though it is less visually appealing. A 1911 with an arched MSH and an old-school grip safety is a handgun that gives me fits. I ogled the Colt Delta Elite for TWENTY FIVE YEARS before I attempted to shoot one and I couldn't get through a magazine without altering my grip!
Back in the day, 1911 shooters wrapped rubber bands around their guns and the more serious 1911 gamers simply pinned the damn grip safety in so it never entered the picture.
On the XD, I believe it is a FINE selling point to at least a decent portion of the market they hope to sell to -- and I definitely do
not mean to insinuate that XD owners active on TFL are representative of that market, but I do sincerely believe that a big part of the XD sales market are the "first defense handgun" buying market that has to walk up to a gun counter and choose between a Glock, M&P, XD, or one of the cheaper "also rans." A gun "salesman" can make quite a pitch in pushing that grip safety. To folks new to handguns, it probably seems like a
magical option that cannot be ignored.
Honestly, if I had to find the best place for a grip safety on handgun, I'd have to say on a supreme, high dollar target pistol with a phenomenal trigger. I appreciate a fantastic trigger on a fine gun and I'm from the camp that wants a
very average trigger in a defense gun. I also hold firm to the idea that if it's polymer, it's a working defense or duty gun or it is a gun I don't want to own in any way.