The SpeedyBit website re queues your transaction but it still doesn't change the fee or priority. Each block only allows a specific number of transactions so those with higher fees will take priority. Using SpeedyBit will give you priority over other low fee transactions. For a better chance at confirmation we recommend accelerating your transaction every 6 to 12 hours.
Also, keep in mind when accelerating transactions. At off peek times lets say around 2AM will give you a better chance at your transaction being confirmed because there are less transactions on the network.