I got PCAT Destroyer last summer from some sweepstakes thing on this forum. As far as I can tell, it's broken up into 5 math/science sections and gives you tons of questions for each with solutions at the end. I can't say how it compares to Dr Collin though.
I am using the PCAT destroyer right now to study for the upcoming test. I believe it to be a strong book but just a bit heavy on the orgo. The way the solution are written are great because you learn extra information even from the wrong answers. I am also using kaplans book to refresh my memory and i believe the two compliment each other well. Just know the the bulk of the destroyer info will come from the solutions and i am very pleased.