I am happy to give constructive feedback at a milonga, but only if it is asked of me. Otherwise, no way.
One sentence solutions tend to be no solution at all, and usually what i feel when dancing is the consequence of a cascade of things and what i think is the root is probably just an intermediate step (i really admire the old teachers who are able to diagnose the root of problems immediately). And to figure out what is actually wrong requires concentrated work from both of us, not something we could do while actually dancing.
So the only thing well meaning advice without actually working on it does is to disrupt an usually perfectly salvagable dance, without giving anything positive back.