I actually like the 2 x 8m FTP test. It seems to produce what seems like the right FTP number for me unlike the 20m test which I struggle to pace or the ramp test which doesn’t seem to suit my physiology and under-reports my FTP (despite it being an all-out eyeballs bleeding, max HR effort).
All this means that one’s results may vary and with estimations getting as good as they are, you may as well take those if they ‘feel’ right.
But, still. 4 x 8m max efforts doesnt seem like it would be a regular feature on my training plan.