I had one of those Bats from Uldaman. They are Huge even when tamed. He is rather Wicked looking, but if hes in front of you beside you around you, good luck at seeing whats going on. He is just..... HUGE. I got rid of him shortly after for a 1.3atk Cat.
I am currently on a personal goal for Snarler. Then at 43 i will have King Banglesh. Haven't decided if im going to go with a AC pet or not. I had a Scorpid, but dropped him to learn Bite 6 from a Longtooth runner in my search for snarler. WOlves are suppose to be "All around pets" so i might just use Snareler for my tank, and King Banglesh for my DPS.
Back to subject, can't say about pet growth definite or not, Ive had a wide variety of them. None for longer than a few levels though. BUt i have noticed the pets I have now are bigger than the ones at lower levels. Like coming over my knee caps. But i just figured it was the kind of cat. /shrug