Against mages with secrets, I think this is a pretty decent card. It'll usually eat 1 secret, occasionally 2, and rarely 3. Worst case scenario, it eats 1 secret and you get a 3/5 for 4 mana, which is not horrible but not great, but also destroy a 3 mana card for your opponent. Pretty decent value.

Against hunters with secrets: Meh. Pretty much the same situation as mage, but since hunter secrets are generally weaker destroying those secrets just isn't worth as much. Still okay, but not in a "oh hell yeah I'm so glad I have this card in my deck" way.

Against paladins with secrets: Pretty phenomenal. The only pallies that really run secrets these days are doing so through MC, which means that this card will usually be eating 5. You get a 7/9 for 4 mana which is phenomenal (and survives trading with MC) while destroying all their secrets. Great card there.

Against every other class in the game: it's a gnomish inventor without that pesky card draw; a worse version of a card that already sees very little play. Not quite as bad as flare where it often might as well say "pay 2 mana to replace this card with something else" as you get a body for it, but certainly below the power curve.

My issue with this card is just that while it seems pretty decent in some situations, 6 of the 9 classes have no secrets and those that do often don't run them. Given how rarely this card will be desirable, I feel like it's somewhat similar to Light's Champion: occasionally a great card to discover, but not something you'd generally want to include in a deck.

I kind of wish they made the base stats a little stronger and the battlecry a little weaker so that it would be about as powerful in situations where it's useful but less crappy in situations where it's not. I just can't see myself putting a card in a deck that will be pretty crappy in probably 75% of the matchups I see, even if it's pretty good in the other 25%.