Wifler MP-one magnetic button.  Only reason for selling is I've bought the MP-Two.  Easily the best button on the market, no springs to change, unaffected by weather and ultimately adjustable, used by the top pros.  Used but in reasonable condition with some small scratching, see photos.  Less than half the price of new - £55 plus £4 postage by bank transfer or if you prefer PayPal if you will pay the seller's fee.