I too was required to wear the shoulder strap on my flight in F from SFO-FRA in the new config about a month ago. The FAs seemed confused as to whether it was truly required, but in the end they found the new rules and said yes, you MUST wear the strap during takeoff and landing. It was a bit of a pain because the shoulder strap is retractable, so always pulls on your seat belt. But after takeoff, you can detach the shoulder strap and just use the bottom seat belt.

The seats in new F are at a VERY decided angle to travel. On the right side of the plane, they face to the left (your feet are to the left of the person's body in front of you). And in the 747, towards the front, the angle of the plane makes the seats even MORE angled left. For me, it was rather uncomfortable during take off and landing because you are at such a strong angle.