I have a little bit of experience with mulching kits and 42" decks...... I had a Toro SS4225 with the recycler kit which is basically a new set of low lift/mulching blades (different in overall design and relatively flat sail) and baffles in the deck to push clippings down. The kit worked VERY WELL with few noticeable clippings. The secret to the mulching kit is to cut ONLY when the grass is dry, to never cut off more than 1/3 of the grass blade length, always run at full throttle and drive at half of maximum ground speed. On my Toro, which had the smart speed system, I could only mulch in the middle setting which was about 5mph. So, to answer your question, they can be good if they are proper mulch kits. The issue with stamped decks is that the clippings will still move from one side of the deck to the other. A fabricated deck with almost always have metal pieces that separate each blade into its own chamber (these are the best kinds of decks for mulching).