For those who want it, here is some data on our turtle mage friend here. For each hero, I'll reveal the chances of Primalist offering a card that will give him value, and some comments on the class in general.
TLDR: Only Druid, Mage, and Priest can ever hope to use the card with any degree of effectiveness. Maybe Rogue or Warlock if you have a really weird deck.
Druid: 69%, by far the highest chance of him being worth playing, he can pull a large number of useful cards that are guaranteed to help, even when cast randomly, including a lot of minion summoning, drawing, and buffing. The best card you can get is usually Wisps of the Old Gods, with a 9.7% chance of it showing.
Hunter: 25%, you can get Call of the Wild 13.6% of the time, which is amazing, but there is not really anything else that makes the card worth playing, mostly secrets, which are not good value.
Mage: 49%, it's worth noting that with mage, while you have only a little less than a coin flip's chance of getting value, when you do get it it is often in the form of Flamestrike, Blizzard, or Greater Arcane Missiles (about 27% of the time), and when you don't get it you will at least get a secret or better 90% of the time, making a true dud more unlikely than with any other class.
Paladin: 35%, and you will get a set of 3 lovely duds giving 1 or less value to the card 39% of the time. You can get Avenging Wrath just under 10% of the time, but that, Lay on Hands, and Stand Against Darkness are the only cards worth getting at all. One of the worst classes for him all accounted for.
Priest: 42%, but with Free From Amber and Mind Control being options, it is still a potential monster if luck is on your side. Furthermore, a lot of priest cards can be interesting and situational, making the chances of it being useful more than what the 42% based on card value and targeting would imply.
Shaman: 33%, and the highest chance of doing something actively detrimental to the player who used him of any class. Overload is a *****, and the cards that might be useful are limited to board booting effects like Spirit Echo and Bloodlust. The best you can really hope for is four murlocs.
Warlock: 12.5% chance, the chance of getting Kara Kazham!. No other card makes it worth the cost of the card without there being a better option to just have in your deck normally. What I mean by that, is that he has a 32% chance of giving you a complete board wipe, which can still be useful. Basically just an unreliable Twisting Nether, don't play him if you are ahead. Or put him in your deck.
Warrior: 12%, very similar to Warlock, only good card that doesn't clear is Ironforge Portal. MAYBE Sudden Genesis. Other than that, a more expensive Brawl is the most you can hope for. If he wins the brawl though, that would give him a moment of glory.
In summary he sucks, but if I see him drafting arena for Druid, Mage, or Priest, totally grabbing him.
Let me know if you want more stats, you single person who read this.