Yeah, the idea is that you don't TEACH the rote method, but that they will notice the pattern themselves after doing the grids a bunch of times.

And in the meantime, even if it takes them ages to notice that, they're practicing and reinforcing the fact of what multiplying fractions actually MEANS (ie, a fraction of a fraction).

I think that eventually, after a certain amount of time, if they haven't noticed it themselves, it's okay to point it out... maybe with some leading questions. Give them a clue that there's a shortcut if they look carefully. But only AFTER they're comfortable with the actual concept of what multiplying fractions means.

Obviously, they can't draw grids for their entire math careers -- the point is just that, like pretty much EVERY other algorithm -- it's important to understand the actual CONCEPT first, and the algorithm shortcut is derived FROM that, rather than right away just teaching the algorithm which on its is devoid of any true connection to the concept, it's just a rule to follow with no real meaning.