It is a shame, because they are unique. I've long since accepted I won't get them (unless I get a large sum of money very suddenly!). However, despite being unique and kinda cool... their models are very very dated. Compare Mini-Diablo to even Mini-Tyrael from 4 years later. HUGE difference. While it would be nice to have a Zergling to join my Baneling in my mini swarm... the Baneling just looks a lot better.
I'm not sure there is a point that I'm trying to make here, other than wow, pets have come a long way.
(Also, Blizz needs to let Grunty fight Banelings too!