yeah, crema-enhancers/pressurised portafilters create back pressure, not to deal with a lack of brew pressure (look at the advertising: 15-17 bar pumps), but to deal with bad coffee and bad preparation skills. (How many people do you know who tamp with the back of a spoon, if at all?) If I recall correctly, vibe pumps won't run at a set brew pressure, but will work up to the pressure needed to brew. So if you get things (grind, dose, distribute and tamp) right, it will brew at about 9 bar. If you pack in too much coffee too tightly, it will stall the pump, or brew at the maximum pressure ... 15-17 bars. But if you use stale old coffee, ground for plunger, not tamped etc, yeah, it probably will brew at a lower pressure. The funny thing is when you try getting crema out of a commercial machine using stale supermarket coffee. The coffee from a pressurised pf looks much better, but they both taste like garbage!
