This guy seems to use something like martingale but seem to be succesful: http://www.myfxbook.com/members/FXViperTrading/fx-viper-live-master-account/616112 He keeps adding positions in one direction and taking small profits. But right now he is shorting the EUR/USD with a big negative position: I don't like this trading style but has made money. If cut the losses right now, he still will be 100% of equity gain.
I know Jeff, he is a good trader. The outsized reward:risk is unpalatable for me personally, but he certainly is an experienced professional who knows what he is doing, and he has a large base of his own funds at risk.