My take on NPP:
It's got less Progestin sides than deca, and it's fast acting so you can control your blood levels easier (further lessening sides), and it's faster acting nature allows you to stop it, and the sides would stop and it would be out of your system within a week (WAAAAYYY faster than deca.) They say that any nandrolone's metabolites stay in your system for a long time, but ive seen no conclusive evidence suggesting it.
My Personal experiences with npp:
The gains are nearly identical to those of deca, but you don't bloat half as much. And with deca, I usually have to keep caber on-hand because of it's progestin sides, but with npp, I can breeze through it at a little bit of a higher dose and (usually) be fine with just vitamin B6. And npp also almost completely relieved my joint pain