One potentially very good thing about LMAX is that it is a multilateral trading facility (or MTF for short) and not just another ECN forex broker.

According to their senior management at the time of the launch LMAX's liquidity providers (or "General Members" in MTF parlance) are not allowed a "last look" before ultimately deciding whether to take the other side of your trade or not. In theory this means LMAX provides all the advantages of an ECN but without some of the disadvantages such as unanticipated order rejections.