I used it once. My avatar was a maiden bitch then who didn't go into heat very often or at a good time. She had 3 pups after the ovuplant. She has gone into heat twice after that when I could breed her. She had 8 and 7 in her other litters. All breedings have been with frozen semen with the same doc doing the breeding.
My feeling is that when we mess with mother nature it usually turns out inferior to what she planned.
Do a search on ovuplant, you should find more.