Back protection - backpack or vest?

Looking to potentially get some back protection. Not interested in the debate of whether that's a good idea or not.

But....

Any thoughts on whether the integrated protection backpacks (e.g. Evoc) offer any disadvantages in terms of effectiveness? Obviously the plus point is they are easily removable on a hot day, and are a "pack" which you'd likely be carrying anyway (unless you were competing).

Plus, any recommendations for specific bits of back protection kit (irrespective of the style)?

Thinking of something like http://www.evocsports.com/bike/protecto ... ckline-16l as a packpack or http://www.evocsports.com/protection-we ... t-lite-men