so many theories here. it is plainly wrong to assume that deca will give you DD.
some don't get it. also there is a statement, that regular long acting deca will give you dick, while NPP, won't. this also doesn't make sense pharmacologically speaking. if you inject daily NPP for weeks, it will have the same physiological effect//metabolites as the long ester. the long one will release it slower into the system, and the effects will linger longer.
and finally, i wouldn't be surprised if many men get deca dick, cause they read some horror stories online. then, maybe they had some ED issues in the past (or not), don't get a good erection and instantly come to the conclusion 'yes, I have deca dick now', therefore its true.
i think all in all, despite being a band-aid for joints, if it helps, it might be a worth a try. as it seems to shut you down, it would be probably good only for men on TRT.
i've seen reports of it working for joints at doses as low as 10mg/week, so this might be highly individual as well.