There is a thread about COMAT exams here -->
http://forums.studentdoctor.net/showthread.php?t=853786
I will say that although they are not nearly as well-written as UW questions, they aren't as horrible as I was expecting. Yes, they're vague and sometimes tough to sift through (reminiscent of Level 1 questions) but I think that on the whole they reflect the information you study.
They are notorious for having information that you aren't going to find in any resource or read about anywhere. These types of questions will be on both COMAT and COMLEX. Just deal with it and move on. Everyone else is going to guess at these as well. As for the other questions, they
generally reflect the specialty they're covering.
I've scored extremely well on all of them and only used Step 2CK resources (which is really all that is available). Because I've used CaseFiles, PreTest, UWorld, Blueprints, etc., and scored very well, I think it's safe to say that if you study hard on your rotations you can do well on them. It's really up to you.
But don't go into them expecting to see the level of thought required by UW questions or that type of great question writing. They just don't have that.