I have shot the Herculiner on a Craftsman riding mower deck bottom and top for a neighbor and this is what Ive discovered after two years:
1- The most noticeable and immediate difference is the sound deadening. I'd guess it dropped by 50%!
2- After the first year, and she brought it back for some routine maintenance, I suspected that her gravel driveway did, at least, some damage to the coating....but not a chip, ding or blemish could I find.
3- From the above examination, I also discovered that there wasn't the slightest trace of moisture, water or rust - And in this area they rot away in 4 or 5 years if the mower isn't washed/dried and kept in a shop or garage.
4- It does NOT make it any easier to wash away grass clippings. It is no more difficult to remove then the OEM finish but the accumulation of 'stuck' grass does not eat away at the metal when you've applied the bed-liner.
IMO, it's not a waste of money with all the added benefits but if you're after something to make it easier to remove caked grass from the underside...then maybe it's not what you're after.