"Just fold the tabs and slide the top of the closest tab half into the slot"
Yes, it can be difficult to assemble, but once you figure it out, the process itself is quite easily. Just "fold the tabs up and out" towards the walls of the helmet, slide the top of the half of the tab closest to you into the slot on the helmet, and you'll find that it slides down into place. It's not entirely intuitive, but reading the directions very carefully will help. The same applies to adjusting the helmet.
It is a fine quality product, and I would recommend it. Beyond assembly issues, the one qualm I have is that it feels a bit too large for me, but it is still quite secure and adequate for protection.
EDIT: Okay, I was actually wrong when I said "slide in the middle of the tab", I guess I was just as confused as well. I've corrected this review, and even uploaded a picture.