The average user takes their gun from their safe, puts it in a rifle case, and takes it to the range where they shoot off a bench a few times a year. That's the extent to which it gets used. Mlok is more secure than keymod, without a doubt. That being said, the stuff isn't coming loose just from hitting it against something unless you REALLY smack the shit out of it.

While it's anecdotal, I've still got some keymod rails on my older rifles with attachments. I've run them moderately hard through courses and banged em around. They've always stayed secure. For a duty rifle? I'm going Mlok. For the average user who will shoot maybe 200 rounds a year through it? Keymod is just fine.