I don't bother with varistream or ecoflo, I have an inline tap set between the van tank and the pump, and mostly have it set so that I'm using mo more than about a litre and a half of water a minute, might even be less than that.
I know that using the likes of a varistream is good for the battery as the drain on it isn't so great, but apart from that I don't see the point in using one.
My pressure switch on the pump never cuts in (unless I disconnect the pole hose from the microbore of course) as the flow isn't restricted on the pressure side of the pump.
Ian