Chris told me he has a Lasermax in a Sig. I too wondered about #2 happening and asked him about this. He said he didn't have an issue with it turning on inadvertently. The other concern I had was with the slide spring. The Lasermax comes with a replacement spring that you have to use in place of the spring that came with the pistol. The Sig spring is braided and supposedly that contributes to longevity, which is one of Sig's strengths. The Lasermax spring doesn't look as robust as the stock Sig spring to me, but the handful of people I've talked to who have one have reported no issues.
Nevertheless, I personally don't like add-ons to pistols that increase their form factor. I haven't heard much negative talk about the LaserMax, so I'd be willing to try it for this reason, armed with the realization that there's almost no such thing as a product with more than one component that's immune to failure.