I run Gator mulching blades on my ZD mowers without actual mulching decks and I like them for several reasons. They definitely chop up grass finer, but not as thoroughly as a mulching deck. With a discharge chute cover they mulch as good as a real mulching deck, but it leaves a windrow at the discharge cover.
When I'm mulching leaves I generally splatter the windrow back into the uncut area with the gate open.
The Gator G6 blades also keep an edge longer than any blade I have tried. I sharpen them every 40 hours or so, and currently run a set with over 700 hours on them.