It is an interesting question, because of the popularity of spinning and the fact that many major driver of the spinning type classes frequently in the winter.
I think most people can benefit from spinning classes. Spinning bikes are to ride two different bikes racing bike, but the physiological adaptations are necessary adjustments to road cycling close. Thus, it is almost certain to improve the performance of his bike when he in a spinning class.
Although I must say that it is impossible to compare 1 hour to 1 hour spinning road cycling. There are many external factors that affect your perceived exertion (temperature, humidity, music teachers, etc.) Therefore, it is very likely a subjective feeling that he has worked more than they are objective (a power meter might tell a different story .. .)
Also, remember that the teachings are fitness-round with the people in the eye. You want to talk to and people who enter the fitness room, once or twice a week, not the cyclists, 8, educate train 12 or more hours per week. I do not think it a bad decision, but it is borne in mind when you are cycling on the road with a much larger amount of training and other purposes, with their training.