That $39/month permits several users and access to a lot of fitness classes beyond just the bike. If you've ever hired a personal trainer at a gym or paid for gym classes, you've almost certainly spent more than $39/month, and certainly more than that if it wasn't just for you.

If you just use it for the cycling classes and for yourself, it's probably not a great deal (financially). But if you also do the HIIT, running, yoga, strength, etc. classes and you (like many people) are a bit more consistent with a coach (even a virtual one) than working out by yourself, it can be worth it.

I pay $14.99 for the standalone Peloton app, which also lets me do all of of those classes. And if Peloton raises the price of that app to where I think it's too expensive, I can move to another one without losing all of my fitness tracking history since I track that with my Garmin watch.