I have a mulching kit on my F2688 and like it but I have little personal experience with it on a ZD326. My S-I-L on the other hand does. She has run a ZD326 for several years and eventually removed her mulching kit because she was dissatisfied with it. So, two differnt people, two different opinions.
It really boils down to what kind of mowing you do. If you only mow your yard every 3 or 4 weeks, when the grass gets knee high, then it's not for you. If you want to mow at 100 mph then you probably won't like it. It does really slow you down. The kit keeps the grass in the deck and with heavy, long grass it can load it up and drag the engine down. If you try cutting it too fast it can load up and make the engine labor. If the grass is "junk grass", long and straggely, you don't get a good cut and it may require a second pass. Those are the reasons that my S-I-L hated it. She doesn't like mowing and when she does, she wants to get it over and done with in the shortest time possible. Now, I cut my four acre yard every 7 - 10 days and in places it's far too rough to go very fast without bruising your kidneys and shaking your fillings loose. So, for me it works pretty well. I do have to make a second pass at times to get some of the straggely bits, especially at the outside of the deck or cut down on my mowing width with a greater overlap. With the rings and the blades it does a great job of mulching, grass and leaves. There's never any clumping of cuttings even when damp and it does help keep from blowing dust and chaff all over the place when it is dry. For my type of mowing it works great and I like it and would never have a mower that didn't have one. The same can be said of my S-I-L, for her type of mowing it didn't work at all from a personal preference perspective although it functioned well.
I can't really give you a yea or nay. It all depends on how you are going to use it, what you are going to use it on and how quickly you want to get it over and done with.
