Having never owned or even seen the non-camera Courierware bag, I can't really say what the differences are; sorry. I also haven't used it much without the inserts, but it does fine without it in my limited experience. It's a much simpler bag inside than my wife's Timbuk2, and I'd stick with the courierware myself.
Can't weigh anything right now, but the insert seems heavy. Then again, the bag itself is very light and unstructured, so it balances out. If I was going to the trouble of ordering a Courierware, I would DEFINITELY get the camera insert, and if I hated it, I'd give it to a friend or sell it on Ebay. Again, I feel it's a massive advantage over the naked bag, and you'll only know how it works for you if you try it. It's not particularly rigid, which is why I like it so much-good balance of softness, structure, and moldability of the bag to your body.
My bag has the exterior clips to hold it shut, and it works pretty well--slower than big single clip, but more secure along the fairly long flap on the medium bag. No problems with security of stuff on the inside pockets even when the bag isn't stuffed full.
I like the stabilizer strap, too.