Int can't be reforged. So you'd have 2k mastery 20 out of every 90 seconds. That's an average of 444 Mastery, but averages don't matter much in this case. When the trinket isn't up, you get no benefit from the slot at all, whereas you could be getting http://www.wowhead.com/item=62471 instead, which would give you 321 passive mastery and the ability to negate a lot of spell damage on a 1 minute cooldown, which interestingly, is less that the trinket you're mentioning.
Originally Posted by Bana
Kathy, I said, "I'm lost" though I knew she was sleeping
I'm empty and aching and I don't know why
Counting the cars on the New Jersey Turnpike
They've all gone to look for America