I am not pro whatsoever and neither have I found a person or situation with Neptune composite in 5th, wait I have.
Well both have its good and bad. It can either be rosey eyed for both or one individual while the other one lingers or it can be a deceptive kind. It really depends on the interplay of the aspects applying to it as well.
Neptune in the 5th can create children who are artistically inclined which is nice
Among many other life's facets.
Neptune in the 7th can among other many facets of life effect a partnership or marriage in which emotions of the mind, fantasy play a role in shaping your world view of each other or decisions you make of one another. This article is pretty Saturnian in its explanation of Neptune which really *****.
I don't think Neptune is a bad thing whatsoever it is more to me a fantasy driven, wishful thinking of life that eludes us from harsh reality and we need it. So don't think about it as negative.