My P1 spider lusso headrests didnt adjust but I carefully bent mine forward (about an inch?) as it seemed far to far back (read about it in a thread here) I have to say I have no wiplash after my accident so guess it did its job.
My original seats did have height-adjustable headrests - they kept wriggling up and blocking rear visibility. I have since fitted some red Momo seats from an older car and they don't adjust. Some advantages but I do worry that they would be less protective of whiplash injury.