I picked up an SB20 a few weeks back and have been using it with Sufferfest using an iPad. I haven’t encountered any issues with the bike, or with integration with the app. As mentioned in the DC Rainmaker review, the one thing you’ll notice is that Stages doesn’t seem to smooth the power data in the same manner as some competing smart bikes. I am ok with this as I think it’s showing the reality that I don’t have a perfectly smooth and even output. I don’t believe there is any similar cadence limitation as I’ve been at least into the 150s and I believe the 160s. I haven’t done Team Scream, so can’t comment on that specifically, but it reacts very quickly in ERG mode.
I can’t compare to other smart bikes, but I find that ERG mode reacts pretty quickly to both changes in power the app is targeting, and my cadence changes. It will fluctuate above and below the target when I am adjusting to a new target, but now that I’ve gone through enough workouts and am familiar with how it works, it’s very quick and smooth to get me to the target. For something like a 10 second sprint or shorter, it’s not going get me exactly to the target, as I am not nearly skilled enough to get my output quickly and smoothly to the new target, while the app/bike are also trying to adjust based on my changing output and cadence. For anything longer, I find it very easy to settle into a groove where variances from me are adjusted for by the app/bike and I’m consistently hitting my targets. The one issue, which doesn’t bother me much, is that with the heavy flywheel, you will overshoot your targets for a significant length of time when you have a large drop in requested output, say from 500 to 150. This can be alleviated by using the brakes to slow the flywheel enough to scrub off the momentum and allow the bike to get you to the target more quickly.
Is it perfect? No, but I’m not sure that is possible as the app/bike can’t know what variations there will be from the user throughout each pedal stroke. I don’t know the specifics of how each app and each smartbike/trainer adjusts, but I think it would be nice to have some user settings where perhaps we could adjust the speed of reaction, or set the bike to adjust so that the user hits the target output if they hit the target cadence. As it is now, the bike is adjusting to me at the same time I’m trying to adjust to the bike. I focus on hitting the target cadence, and just allow the app/bike to adjust so that I hit the target output. That is working very well, but there are fluctuations that I’m sure bother some people, who expect to have perfect straight lines at exactly the target. After a couple dozen workouts, I haven’t had one where I felt that the bike/app weren’t able to put me right where I needed the resistance for every segment.