I have the JOF 55. I've tried the Sitero. I found the Sitero to be uncomfortably hard. I find the JOF to be a little too soft at times (so I sink in a bit). For me, the JOF could stand to be just few mm more narrow and slightly more firm. I get some rubbing on the side of my groin area from it. I like the JOF better than the Adamo Prologue that came with the bike. I had the Plus and the Max as well. When I'm fatigued in the JOF, I feel like I want to rest in the aero position. When I am rubbed sore from the Max I feel like I want to end my ride early. Personally I'm still not 100% satisfied and think I will try a Dash and perhaps find a more narrow Adamo. Sometimes I wish I had a Ken Doll-like underside so this whole process would be more simple.