I don't trust the strips these days... I find that they're in the ballpark for light colored beers after Kai's correction of .3, but they still underestimated pH for dark beers. This leads to the worst possible "remedy", adding extra alkalinity. Plus, estimates aren't that helpful. I either want an accurate reading for a new recipe to make adjustments or I'm going to let it ride.
I've tested them against my meter a few times, and I've found them to be pretty accurate once I apply the correction factor. Mostly, I just find my meter to be a pain.
When I brew darker beers, I usually don't mash the dark grains; I just add them during the sparge, so it's not much of an issue. I rarely find the need to add additional alkalinity, even though I mostly brew with 100% RO water.