This evolutionary development seems disadvantageous... I mean, sure a cock that sucks (literally) does seem oddly sexy, but it seems to me that if the human body had to create that much suction to ensure pregnancy, the race would die right out. ...To say nothing of what it would be like to give birth through a penis. Also, I'm not sure what her testicles are for since the cross section shows he has internal testicles and her ovaries are still in the normal place.
There's also the matter of the male storing the testicles right inside his body. Wasn't the reason we store them in vulnerable hanging sacks to have better control over their temperature by changing their distance from the body? Can't do so with them stuck inside like that.
For those wondering, this setup is similar to barklouse dimorphism. The female's organ locks into place with the male's, using the spines and ridges on it to stimulate ejaculation in the male. In the insects' case, though, this takes over 70 hours.