Poorly designed and poorly produced. You must adhere the "T" , corner, and cross sections first and then cut the cross beams to fit in between these. The problem is that they built the cross beams thicker than the other sections so they stand proud. At this point there's nothing you can do! You can't sand them aggressively because it's a high-density foam. You then end up trying to use a ton of putty and sand each of the intersections (62 for my ceiling!) many many times to try to get it to look right. In the end it still looks horrible, but you're stuck with it.

Great system for a coffered ceiling