Just to put another slant on this: a couple of years ago I was fitting out a van and the pump/controller unit wouldn't work. I bought it from Cleaningspot. I rang them and they put me onto Williamsons, who told me to send the controller back and they would test it, but warned me if there was nothing wrong with it they would charge me a test fee. Can't remember what the fee was but it wasn't cheap.
A few days later Williamsons rang to say they'd had the controller on test for three days and it had worked perfectly.
In the meantime I had completed the van fit-out with the same pump but a different controller I had in stock. The unit worked perfectly.
I got the faulty controller back and fitted it with another pump - it worked perfectly

I never did find out why it wouldn't work with the first pump, but both systems are still working fine.
I had to bite the bullet and pay.
I wouldn't buy another controller - you can set your pump to a reasonable flow by adjusting the pressure control (on the bottom of the pump - a screw that you turn to increase/decrease pressure) and then use it wired direct to the battery with a simple toggle switch to turn it on or off. No need even for a by-pass valve as you have just the right amount of flow to suit you.
These controllers came in long after we all started using WFP, as an "add on" to improve performance, but they're by no means an essential part of your system.