I've had very good results with the AT875r as a cheap but decent sounding lightweight camera shotgun.
It's smaller, more rugged, and I think better sounding then the Rode ones.
And its pickup pattern seems to be just right and versatile for most guerrilla doc camera-mic-is-the-only-option scenarios. Narrow enough to get a decent sounding interview with a single person directly in front of camera. But wide enough to decently capture a whole room, group of people, or some sort of event or ambience.
I don't think putting an expensive mic on the camera is worth the risk vs. sound quality gained. It's on the dang camera anyway so it's never going to sound great. It feels much better putting a $160 mic on the camera that still sounds decent.