It all starts out very civil. There are some jokes about how it is going to hurt, but that you (the rider) will achieve a better metric for training (and current fitness) then you would obtain from a conventional FTP test.
There is music (it is OK, but for most of the hour long session the fan obscured the music enough that I could ignore it).
There are racing videos (the one of Sagan going on to win something on cobbles was a favourite).
On the top of the screen are three displays: heart rate (blank for me because I do not own a Bluetooth HR belt), cadence (blank for me too often because I had the Wahoo cadence sensor in my sock, and it doesn’t work perfectly in a sock - it reads above 95 perfectly and not at all below 85) and power (coming from the Kickr).
Under that is a progress bar that counts down through the current effort.
At the bottom of the screen is a trace of relative effort levels the test requires. This is replaced by a green line of actual power levels as the hour passes.
Music titles flash up as the song changes.

The order of things is two sprints of 10 seconds each with a decent recovery in between them - to determine maximal anaerobic power (they call it neuromuscular power, NP); then a 5 minute “uphill” TT effort to determine maximal aerobic power (MAP); a really good break follows that, including a walk off the bike for 1 minute; the 20 minute TT effort is third to determine functional threshold power (FTP); the same break as last time provides inadequate recovery for the final 1 minute effort to determine recovery ability and aerobic capacity (AC).

By the conclusion of the 1 minute effort I couldn’t function. I put it all into that test.
It is hard.

The FTP score I got was about in line with what I have seen on the trainer before, but is low compared to an outdoor value. Some of my clients are closer with their scores (indoor:outdoor) but everyone goes worse on the trainer. Even with the big fan the cooling is not as good. The rigidly fixed bike doesn’t help either!

Sufferfest has a snazzy graph to present the results. It is 4 concentric circles cut in half horizontally with the top half further divided into 3 pie wedges. The bottom half is the FTP score (the main driver of bike racing successes) while the other three factors are across the top.
The inside circle is “needs improvement”; then “good”, “very good” and the outer circle is “exceptional”.
My MAP score is just over the good line.
My NM and AC scores are half-way between good and very good.
My FTP just crept over the very good line.

Traditionally I have had a hard enough time getting clients to do a field test once per month. My field test is two TTs of 5 km each done back to back. I am quite certain I could not ask most clients to do this regularly! It is heinous and they’d all leave.

The best part of the experience was how they timed a bike race video to end exactly at the end of each segment. Visual assistance to really get into the effort. Sprint with the sprinters - that sort of thing.

It will never have the interactive appeal of Zwift, but Sufferfest is pretty cool.