They sometimes don't have the vouchers and without the voucher, even F boarding pass doesn't let you use it, so it can be pretty bad. One of my fellow passengers in F got refused because he didn't have the voucher, and I tried to vouch for him in Japanese that he was a genuine F passenger who happened to be seated across the aisle from me (I was given a voucher on board but I specifically asked for it), and he showed them his F boarding pass, and they still said no. So there are still difficulties with using it from time to time even when arriving in F.

I haven't yet come across any airline that gives it to non-F passenger. I hope they'll start once they start getting a barrage of complaints from their passengers about the long queue and the lack of fast track access.

(It still won't solve the problem at HND due to being completely devoid of fast track immigration though.)