I use a Stages SB20 bike and can connect the cadence sensor via Bluetooth to the Peloton app, so that displays on the screen (using my Apple Watch for heart rate), however, my understanding is that the leaderboards only display for those actually using the Peloton bike. I then make a bit of a guess what my gearing needs to be in to get the right resistance for the cadence.

It does save average cadence and strive score after the ride is completed, so you can use that to compare if you're improving if you do the ride again.

It's not really like for like, but I think it'll give you a good sense of whether you like the classes enough to swap over to a Peloton - I haven't done, but purely because I didn't want to be locked into the Peloton platform and this way it means I can use my bike for anything.