A piece of folk wisdom I picked up along the way was you often end up needing a "Behavior a" and an "Event a" that fires when the Behavior changes. The reason I switched from dabbling-with-reactive-banana to dabbling-with-reflex is exactly that I needed "Dynamic"s.The semantics for Behavior require that it doesn't appear to change value until the frame has finished updating, so you either need to keep an Event around that fires the "new value" in the current frame or use a more powerful library.

Remark: Event is a Monoid or a Semigroup only when the contained value is either a Semigroup. The most useful combining ability comes from Behavior's Applicative instance.