I keep my helmet nice and clean by dipping it in parrafin and scrubbing it with a wire brush........
On a serious note, I really miss the BSI/ACU construction regulations. That helmet is possibly only safe for low speed impacts, but you try finding out that information.
I've never owned a £500 helmet, nor could I justify spending that sort of hard earned on one, but I wouldn't trust one of those lids to save me at speed