I’ve done it a few times, once on an MTB with slicks (not recommended, I knackered my knee that way!)
All the times I’ve done it recently have been on my roadie SS but I know plenty of people do it fixed. It’s even been done on a Boris Bike. The distance isn’t a problem unless you set off like a lunatic and die after 80 miles.
More recently, various enterprising locals have set up food stalls in their front gardens. There’s one quite well known spot about 2/3rds of the way there which sells bacon sarnies and coffee from a barbeque in the front garden.
I remember doing it one year and setting off with the Brixton Cycles crew. We caned it out through North London and into Essex, full on chaingang averaging about 25mph. I was wondering how long I could sustain that kind of pace when we reached the pub – clearly the target had been “get to this pub before last orders”. We made it there at about 10.45pm!
It’s not a Sportive in the traditional sense, it’s very much a loosely organised, “anyone can do it” pootle.