Plugging it into the powerbar would only turn the unit on/off by cutting power to the vortech. The Neptune Vortech control module can vary the flow of the pump like the Vortech controller does.
The only real advantage to the module is you are also able to run different vortech modes at different set times. For example, you could run reef crest in the morning and then pusle it for a wave in the afternoon...or pretty much any combo of modes/times you want. You are also able to have the Neptune control all pumps by hitting one feed button, instead of having to hit the feed on the neptune and the vortech.