My wife and I did spin classes for a few years with excellent instructors: a female TT specialist and a Cat 1 trackie of some sort. He could hit 200 no problem. We enjoyed the classes very much, made friends with other attendees, but eventually decided that we need to do our indoor bike training at home so we could periodize our workouts and do exactly what we needed to do.
The other minor issue with spin bikes is that they are fixed gear bikes and thus are much too easy to pedal. One's pedal stroke gets all weird and doesn't translate well to a road bike.
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