Your advice - don't send them shit - is basically the same as their advice, though, just in your case you have a "maybe a meteorite" that you think is valuable, and in their case you probably just have a rock after following the flowchart.

Even their advice if the flowchart says its interesting is to send pictures next, not send it in.

My own behavior, if I sent pictures and they said "yes, that might be a meteorite" would be to arrange to bring it in in person, sometime.

Mailing it blindly doesn't seem like it should be anyone's first instinct, but they certainly aren't saying anyone should do that.