I agree with Powain : They are in reality inferior to most of the trained pets, even when fully trained.
ALSO IN MY OPINION their ONLY good thing is : They are collectibles, a rare pet, that does not spawn. Collectors items. I would NOT train unless like pawain said you trained 20 +pets. Keep the pet indef. in stable, and take it out to impress pple when you feel like it. If I had one, I would do the same, OR sell for 600M-1 Plat, and use some of the $$ to restart your game, get gear, PS, etc. Have fun. By the way if you have old mares they are also RARE now, due to their stats prepatch. These also you need be careful NOT to train right away. They make nice pets. Post all your pets here for ideas and you will get (mostly) very reliable info. HAve fun and GL.