Can't speak for the Kubota but I have been mulching with my JD 60" MMM for a couple of years and I think it's worth the money and effort. Assuming the Kubota design uses the same principles as the JD, you will need to spend a little more time keeping the underside of the deck clean.
You will need to avoid cutting when the grass is too wet. There is a rule of thumb for any mulching deck that you should cut no more than 30% of the height of the grass to get the best result. During the peak growing season I cut about every four days, or so, and never leave windrows or have to bag or rake. Essesntially, the mulching kit will provide a plug plate for the discharge chute and baffles to create an airflow that keeps the clippings suspended under the deck for cutiing and re-cutting. The JD blades have lower and upper cutting edges. I have been told that using "Gator" brand blades with a manufacturers kit is overkill. The resulting clippings are so fine they end up clogging the deck. I think the gators are best used alone.
All in all, I think its the better solution compared to collection systems and my rake handles seem to show a little less wear. /w3tcompact/icons/smile.gif
Good luck