Tau is an army I'm just getting into, so what I understand is... limited.
From what I've read and seen, I agree with Shadowcat. But I also want to say I've read a great deal of positive reviews of Sniper Drones, from both the perspective of controller and opponent. I don't think I've ever seen anyone say they are outright bad (at least not with good reason), it's just that people are either indifferent or can't fit them into their lists.
Also, to add to his critique of the Devilfish. If I remember, Shadow doesn't feel Fire Warriors are well placed right now, so that makes the Devilfish a less than ideal upgrade. However, if you're running Fire Warriors anyway, it is probably worth it.
But get Riptides, Broadsides, and Sniper Drones first.