I bought a Gravely ZT52HD last April. On the salesman's recommendation, got the chute block kit. I figured knew what he was talking about. I told him that I planned on mulching almost exclusively. When I got the chute block kit and installed it, I knew it was NOT going to work for what I wanted to do. In fact, the instructions that came with the chute block kit stated very clearly that it was NOT intended to be used for mulching operations! I removed it before even using it and exchanged it for the mulching kit. It's MUCH better than the chute block!
The mulching kit and original blades works pretty well, even in heavy grass. But about half way through the season, I picked up a set of Gator blades and installed them. What a difference, they work great! They do an excellent job cutting grass, but work even better for mulching leaves in the fall. I have a LOT of leaves to deal with in the fall and was skeptical at first. For years I've used a Trac Vac and lawn tractor to remove the leaves. This past fall, I mulched all of the leaves and they just DISAPPEARED! I was shocked. Go for the mulch kit and get a set of Gator Blades.
You won't be sorry if you buy a Gravely!