I actually have two VIS pumps and there is a bit of a shaggy dog story behind this.....
I originally bought an ‘internals’ kit which I had fitted to my car in July. Whilst fitting, my mechanic noticed that the original pump had a crack forming on the spring retainer collar and that the internal seal was knackered. We therefore ordered a new pump from the local VW dealer and ran the car for a week whilst waiting for it to arrive. During this time, the car (revo st1 k03) ran really strongly in the midrange using the original map settings. After the internals were refitted to the new factory pump, the midrange evaporated despite the car otherwise running quietly with no fault codes upon scanning.
As nothing else had been changed, it was obvious that the fuel pump install was to blame and I reported this back to VIS. They have always been super responsive and, whilst they suspected a faulty installation, they offered to inspect and repair the pump for free. Rather than have my car out of action for a couple of weeks, I simply bought a complete new pump from them (which has solved the problem) and will sell on the other pump once they have have given it the ‘OK’ after thoroughly testing. This should hopefully be early next week and if anyone wants to buy it then VIS could ship directly to them.
Based on my experiences, I would advise that people check their pumps very closely as these faults happened to a very low mileage car (24k) which has always used top quality oil and whose pump had never previously been removed. There is also a question mark over how foolproof installation might be as my mechanic is pretty skilled, albeit not a TFSI expert.