I have one. The answer is they are a good all-rounder. Mine weighs around 1.7kg and is about as warm as a snugpak micro which is 600g or so lighter. I like wool so I enjoy using mine, but as regards warmth to weight they can't compete with modern down or synthetic bags. Bombproof though and you don't have to worry about getting it wet. If you're not worried about weight, they are ideal for late spring through to autumn in the UK.
To protect yourself, you must protect everything that is not yourself.