Just a added note here from experience. I have tried both the Ninja blade and also the Gator mulching blade. I was disappointed with both compared to the OEM Snapper blade with lift wings and a mulch cover. The cut grass is cut/mulched so fine as to simply disappear.The "mulch" blades are hanging in the garage and will never be used again,except in a pinch.
Nice to hear some feedback on the Ninja and Gator blades. I've never used the Ninja blade nor deck. I would like to try one some day if I get a used Snapper to flip. I have gator blades from Oregon. My opinion, Oregon makes the best blades out there. Especially considering cost of the blades. Gators are made to mulch. On a Snapper 21" commercial, I ran the Gator mulch blade and the mulch deck cover. I had no issues mulching.
slomo