I like to do demonstrations for the AR crowd on what they used before they got the 40MM stuff. Most don't know what the heck a rifle grenade is.
I think the Israelis however still use the concept.
Plus if you use an M82 blank, you can do it places you couldn't otherwise shoot because it only goes 100 yards and lands relatively harmlessly. And M82 (or equivalent) blanks are cheap anyway.
The real M64s put a hellacious strain on the stock, are expensive (4 bucks a pop), and shoot the thing way too far!