I managed to get one of the small Ergon ones for half price and use it in place of my now retired Mule. I use it all the time because it a) works brilliantly (smart German engineering types) and b) if you can’t tell a pack has a back protector, why the hell not use it?
I do also have an Evoc 20l for when I need to carry more than water + odds and sods. They look massive but are shallow and spread the load. The protector sits behind a much wider ribbed back. It’s really comfortable and easy to forget. Better still the 20l back protector can be zipped off if you want to use it on its own say for an uplift day at BPW (not so the 16l). Again, brilliant German boffinry. Buy the 2016 version and there’s a revised waist strap and back ribbing for better ventilation.
In both cases I considered a Kudu. I found it was much more of a hump and had less flexible storage.