AON are held by MMs for execution. It would be chaos otherwise. For example: If you placed an order to Buy 1000 shares of EVIO @ .87 AON and I placed an order for 1000 shares also AON @ .86 and a seller came in to sell 999 @ either price, he would not be filled. ALSO- if he (or she) entered a market sell order, it would be filled at maybe .85 and you and I would be upset it traded through us.
AON orders can be tricky business in a thinly traded penny. Generally would have to be bid/offered in size at your price to get a fill unless you just happened to get a diligent and generous MM handling your order. Happens, but rarely. They will use your order to trade in front.