After playing with IK's new Mastering EQ for a little while, I can say it sounds really good. Right up there with the best native EQ plugins like Waves RS56 or even UAD's high-end EQs. Boosts are smooth and clear, without harshness. Overall, a nice transparent character -- hard to make it sound bad.
Now the question is, is it worth $100? Maybe, if you don't already have a high-end EQ like those I mentioned above. But if I wanted to spend that much on a plugin, I'd wait for the next revision of Equavescent, which is still in beta but offers the best sound quality I've ever heard from a software EQ, particularly on high-shelf boosts.
As usual, YMMV, demo them yourself, etc.
Cheers,
Eddie