Bought this recently for my track day and I've not ridden without it since. It's very light and thin so you barely know it's there, except for the waist strap that hugs you like pillion arms. It goes all the way down to your coccyx area and has little kidney protectors and so I feel pretty invincible in it.
For £80 it has got to be worth it. Everyone I know that has had an 'off' has landed on their back, so I was starting to feel a bit vulnerable there.
My only gripe is that because it goes quite low down your spine and I have 2-piece leathers, if I bend down it slides up and then jabs me in the back of the neck if I try and look up - forcing me into a MotoGP style tuck. If I drop my glove or something, I look like I've broken my back; trying to pick it up whilst staying as straight as I can.
Guess it's just an excuse to get a 1-piece now...