So I just finished raising my 75th pet to 25 and got the Pro Pet Club achievement. The reward is the Singing Cricket, but get this, its quality rating is Uncommon. *boggle* It also didn't arrive as an item, but was silently added to my pet journal much as Venus and the Feral Vermling were.
I had some warning of this, as Warla got this achievement a few weeks ago and ran into the same problem. However, I'd assumed 5.1 had actually fixed that. Apparently not.
As far as the pet itself, it's just a green cricket, a smaller version of the marsh fiddler. It doesn't sing or do anything special.
So very very disappointed.