You mean the quite expensive mulch kit. Yes they work quite well and will eliminate most of the clippings. They are not magic though. Mulch kits can cause problems if you let the grass get too tall.

Very few pro mowers around here mulch grass. I have not seen any on their commercial machines. All use discharge and look great. Can't see any advantage to mulch if it looks good.

The reason most pro mowers don't mulch grass is that customers won't allow it -- the uninformed masses seem to think that if they're paying for a lawn service, a complete and thorough job includes bagging and hauling away clippings rather than leaving them on the lawn.

The dirty little secret, however, is that most companies do stealth mulching -- they don't empty the bag when it gets full, leaving the cut grass no place to go, in which case it just ends up back on the lawn as if a mulching plug was installed.

Discharge is the only way to go, when the grass is to tall it fans the clippings evenly and the sun will do the rest in a day or 2. The only time bagging is necessary is if you have a pool and you don't want clippings in the pool. I have never bagged or mulched grass and I always have the nicest lawn. I only feed the grass in the spring and that is it. The clippings do the rest of the feeding

'The dirty little secret, however, is that most companies do stealth mulching -- they don't empty the bag when it gets full, leaving the cut grass no place to go, in which case it just ends up back on the lawn as if a mulching plug was installed.'

Very true and also fairly common practice generally, sometimes unintentionally.