What are the properties of Greenhand?

zangief

#1

I always knew greenhand was punishable on block but the frame data says it’s minus 5 on hit, so does that mean you can be punished anytime you land it? Also I read something about a 1-hit ex greenhand being punishable and I’m wondering how that works ie first hit? second hit? Are there any other weird things about this move I should know about?