P.S.
Meanwhile to make a comment relative to the thread topic(I'm bad about hijacking/sidebarring a thread:0)
I just put a mulch kit on my Gravely which has about 31 hours on it. The OEM blades I removed seemed to still be in fairly good shape and sharp(although not "razor sharp"). As a homeowner, I would lean towards sharpening & balancing blades once a season or every 50 hours(whichever comes first). Even at 50 hours, for a commercial user, that would probably be at least weekly or maybe a little more often(based upon a "40 hour work week", although I'm sure some guys mow more than that weekly).
P.S.S.
To keep with my predisposition to sidebar a thread topic.....check out the link below for something referred to as a "Meg-Mo System", which appears to indeed be four blades in the shape of an X.....I cannot elude to whether it is a gimmick or for real as I have only read one post where a user was asking about them:
Meg-Mo Systems - Lawn Mower Blades, Replacement Mower Blades, Sharpen Lawn Mower Blades, Mulch Grass