"Relatively hung" depends on what you think of as hung. Bonobos go about 3 inches on average. "Friendly" is also relative...youre talking about a creature that could literally tear your arm or face off in a fit of frustration. The apes all have large testicles to produce many sperm, and they tend to mate often but briefly.
Since they are more doggie style oriented, Id think that even three inches might not be sufficient to mate with a human. Our Buttocks are much more developed. It's not absolutely impossible, but the probability of being frustrated IS there. The other apes are even less well-endowed, regardless of size. Its one of those things that should remain a fantasy.