I don't know anything specific about the Prestone Flush. However, any time that you introduce regular tap water into the aluminum North* it can be detrimental.
Unless your sytem is plugged, there is no need to flush.
Agreed with Eldyfig - it will probably do more harm than good. You would have to get all of that stuff out of the system before you go refilling it, and that's not easy to do since there are no block drains. It would take many flushes with plain water to get it out of there, and I don't think it is going to help anything anyway. If I was you, I'd avoid it and stick with just draining and refilling the system. Tap water is not good for cooling systems, and I certainly wouldn't want to put any in my car unless it was the only available option.