I got the Brooks Flyer in the end and have had a few rides with it on my fat bike. It's not exactly a looker and doesn't look great on the bike. It does feel comfortable to sit on. I sense the extra strain on my knees but I think that's more to do with the seat being too low at the moment. I'm adjusting the seat height by tiny amounts after each ride to find the ideal height.

I have a B67 on my cruiser and that is very springy but ideal for the cruiser. The Flyer has almost no give in the springs that I can feel.

I'll see how it goes with the Flyer. The springs reduce the seatpost that visible so make mounting a rear light somewhat tricky. I've had to be a little creative to get my light mounted. It's at the very top of the seapost, literally shining through the springs of the Flyer.

There's no shop nearby that would loan a saddle. I'm basically buying new ones and then selling them at a slight loss as nearly new after trying them out for a handful of rides.