You don't get that issue on digi spring type contollers I use so can't say what varistream are like as never used one.
Going by the other link you posted your using a pf trolley with a spring digi controller the same as mine. I would diduce that you're not bleeding all air out of the system when the containers run dry and/or change them over as is sucking in air so the controller will not work as it should unless you do so.
Hi Smurf. It's me with the trolley. The problem isn't caused by air in the system. I do get that with the trolley from time to time and it just causes weak sputtery flow and is easily fixed by disconnecting the hose at the trolley for few seconds until it reprimes itself and you get a solid flow.
According to Ian Shepherd it's how the controller is designed. And I never had the issue with the analogue version. When shutting off the flow with a long length of mini or microbore connected, say 100 mtr, the pump pressurises the hose and it expands. When turning your tap back on the hose squeezes the water it is holding out first while the controller continues through it's cycle and switches on. So it gives the appearance of switching on immediately when in fact it isn't. That is not a problem for a system that always pushes it's water through long lengths of hose before it gets to the brush. However, I like to work with a short length of PU pole hose which doesn't share the stretchy quality of mini or microbore. So when I shut off my water flow, there's next to no expansion in my hose, so the delay caused by the controller cycle is quite noticeable. However, all that said, I'm now using the univalve coupled with fan jets in my brushes and am finding I'm using a lot less water. So I'm not so concerned with shutting off the water every few seconds now