It’s easy to dismiss the montage. It feels like a shapeless “default” form. As in, “What do you want to do tonight?” “Let’s just do a montage.” This quickly becomes a series of scenes with little connection to one another, that may or may not be apparently tied to the suggestion or opening. It feels like a form without rules, a collection of scenes.
But a good montage has rules, just like the Harold or La Ronde or any other form. The big difference is, in a montage, you make them up as you go, which means you have to actively look out for them.
Montage sounds a bit cooler than freeform, I’ll admit.