It provides you with the ability to present your trade as high bidder, down to lowest offer. This is accomplished by buying at the ask and selling at the bid, or in other words, the market maker is selling you his shares at the ask, and buying your shares at the bid. The advantage of using SOES is that market makers are hit electronically, and thus this makes it very difficult for a market maker not to honor the quoted price and quantity. Selectnet, an electronic order-routing system primarily used by market makers. When you as the trader place attempt to place your trade using Selectnet, your order may or may not be filled.
Market makers have the sole option of accepting the order.
You have the ability to track your order, and possibly be filled instantly, within seconds.