Spin bikes are a few generations behind the state of the art. I resisted spending the money on a smart trainer for years, but then succumbed.

I don't mind doing indoor rides throughout the winter when I can't face the cold or wet, but the little inner voice that wonders whether I should be working harder or taking it easier or doing either for longer or shorter intervals really saps my concentration.

Now, I just fire up Xert (software that monitors my fitness, or lack thereof, and my progress, or lack thereof, and dynamically adjusts the workout accordingly) and do the prescribed workout. The software controls the resistance on the basis of my heart rate, cadence, and power output (and also incorporates the same and other data from the previous week, month, etc.).

Turns out my previous indoor rides on dumb trainers were usually uniformly in the a-bit-too-hard-for-too-long zone, paradoxically limiting my progress. Now, I finish every hard-ish workout feeling moderately fatigued while knowing that the next day's workout will be set in a very easy recovery zone.

Many people like smart trainers for the social aspect of virtual group riding or racing. Tried that once or twice, but it felt too random. I do structured workouts exclusively.