Things I liked: Excellent product. I could not be happier. I've got a fairly custom setup on my AR-15 with a match trigger and the upper fit perfectly. Very easy to use, accurate, and a thorough pleasure. If you are looking to improve your trigger control and overal utilization of your AR platform and don't have a range in your backyard, this is an ideal solution. I have a 10 meter setup in my garage for practice with my air pistols and rifles and the Crosman AR-15 upper is my favorite to shoot. Highly recommended!
Things I would have changed: Nothing.
What others should know: Get the Benjamin hand-pump. I get to about 2,000 PSI with less than eighty strokes.