After doing about 6 years of professional lawn care, i feel i can give you a honest opinion
The answer is not simple however.....
Are mulch kits worth it? - Short answer "depends"
It really depends on what brand mower your looking at.
I, always ran scag mowers. The hurricane mulch kit works amazing. Well worth the money in some cases
Same with exmark, they work well in certain situations
keep in mind that decks are designed mostly for discharge. All airflow must go out for the best cut
Now, downfalls
They dont cut grass even/rips turf since the airflow is disrupted.
Grass must be short, no more than .5" off at any time otherwise it will clump
grass must be dry. any moisture will cause it to clump
Leaves in the fall.....have to go slow to not overload the deck
My honest opinion, if you dont have to do a mulch kit, dont.
They are a pain. Requires constant deck scraping and cleaning, your blades will go dull alot faster as your cutting the same grass over and over.
If your doing it to not get grass in the landscaping, look into a rear discharge deck.
Otherwise, if you need one, id recommend scag hurricane mulch kit with the scag blades. They are offset to give the most volume under the deck (because it will plug up)
When i did lawn care, I ran a toro z 60" turbo force deck with a mulch kit. It was a diesel mower, had torque for days.....
Nice mower in the summer when your cutting very little. It sat in the spring and fall since it clumped so bad.....nobody wanted to use it.