Others on the forum have reported excellent results from their 7-iron decks with the JD mulching kit. But it may be more than just the chute blocker... though I'm "guessing" here - not owning a 7-iron deck myself.
On my (much smaller - 48") JD mulching deck, the kit includes the chute blocker, and some different blades. The mulching blades are actually two blades on each spindle, in an "X" pattern. One blade pulls up the grass and cuts it, while the other chops the "remnants" into fine mulch. (Or so goes the theory.) It does a very good job. If your 7-iron deck already includes the "X" blades, you may be in good shape.
My next-door neighbor has a "regular" deck on his mower, and tried a "chute blocker" type setup that was supposed to convert it to a mulcher. It didn't work at all... It left large clumps of grass all over his yard, where the grass accumulated under the edge of the deck, and finally "rolled" out from under the back of the deck. He was not very happy.
I showed him how my deck worked with the X-blades, and he just kind of grunted, and took the "mulching kit" off his deck.
Ever since, he sprays clippings all over the place. (Usually there are at least two "swaths" of clippings across my gravel driveway.
)
Good luck!
