Chin up, Lu, they are just pulling your p155er.
The bifilars are to reduce certain rotational vibrations. With a 4-bladed system, you would expect 4:1, maybe 2:1 and some 1:1 vibes, but these are tuned to remove 3:1 and 5:1!
And no, they don't rely on precession to do it, there is a really kinky combination of moving weights sliding around on keyways and cams with specially shaped holes. Must have driven Nick mad to get them tuned, but they seem to work. But some operators pull one set of four off and just fly with the other set (in S76 anyway).