It sucks....BAD! ;p
I throw a HR monitor on and ramp my HR to 85% fr 15-20mins, or I do intervals....fuggin really sucks! I started to check my HR recovery occasionally, last week I hit 175 and stopped....feet on the pegs and arms on my thighs @1min I was at 141 and @ 2min I was at 121. According to some references I'm "good" or "excellent". A couple points improvemnt over the past 2 times I did a check. I dunno how good it is, but I figure a baseline of 30bpm@1/50bpm@2 is a good to judge improvemnt.
20 mins is my limit for attention span on it. I move on to hitting a few movements on the TRX mostly the last couple months. When my shoulder feels better I'll hit kettlebells again.
It really is a good low stress body workout, I have shoulder, hip, neck, knee and ankle issues and the bike makes a good intense workout w/o too much stress on joints. It is solidly built, I wish the readout was illuminated, I workout 2 or 3 times a week early morning while still dark. I wish it had more fan blades to make it even harder to move, so I could have lower RPMs......I think I'd like having more ressistance even though it is kinda hard already. Not sure if that would be good, but I'd like to try it. I don't know how it compares to an Airdyne, but internet users seem to say it is harder.