Well, there were a couple of reasons why I skipped their greylisting.
1) Their greylisting is a bit different, and would prove to be redundant most of the time. In otherwords, the method I provided already blocks almost all spam. It would add to the delivery time and would have less than a 1% additional success rate.
2) Their greylisting technique isn't the greatest. There have been a lot of mixed reviews and some of their own developers mentioned that it's a hit and miss, at your own risk endeavor.
So, I figured with those two reasons (and some minor things), it's not worth adding to the email delay and using additional resources vital for other server tasks for no more than a 1% gain in most instances.
If you have a robust server and don't care about delays or possibly having extra misfires, then it would be fine to use IMO.
That answer it decently enough?
ISPC3 on Debian! It's great!