Sadly, I reckon they are absolutely a 'novelty value' pet, at four slots. They can do a reasonable mana dump to start off a fight, but apparently can't handle things that survive that. I can't even think of good one-slot pet to pair with them and cover the deficiencies skree have.... even were they to drop to a 3 slot pet, I still have trouble working out how they would do well in combat compared to other choices out there. The only thing I have not tested is they might, possibly, magically heal other pets or their owner? I've seen no sign of that so far though.
I'm inclined to say 'great pet for RP and fun value', but I can't see them appearing as hunting companions any time soon. I want to train one up simply because I reckon they are remarkably cute, compared to most 'practical' pets, and I have a RP character that they would be a perfect companion for.
Harlequin, good sugestions - I've not had any luck with 'matched skill' opponents, and trained both outside and inside my house, but my tamer is pure mage/tamer so I'll have to see if I can get a friend to tag along with a bard and test the disco idea out a bit.