It's a very nice trinket. Agility and crit are both wonderful stats for reducing the damage we take. That said, since crit is kind of an indirect method of reducing damage (it builds more EB stacks which are then used to reduce damage via a dodge buff), having it as an 'on-use' doesn't work as well as, say, a direct dodge or parry cooldown for a plate tank.
So what you could do is macro the trinket into your Jab, which will then ensure it's used ASAP, every time it comes off cooldown. This has the reduced benefit of sometimes being horribly mistimed (jabbing just as you get banished on Gara'jal, for example), but 9 times out of 10 this will work just fine.
Alternatively you can just manage the trinket yourself manually. An extra thing to keep track of on a tank which already has a ton of stuff to watch, but less chance of it being wasted.
Personal preference really. In short, yes the trinket is very nice.