Nothing will overlay into the fitness app. If your bike doesn’t have one built in I recommend this, Wahoo RPM Cycling Cadence Sensor https://www.amazon.com/dp/B00L9XNFPY?ref=ppx_pop_mob_ap_share I’ve got a barebones Sunny bike which I love and using this cadence sensor I can watch the video on my phone or iPad and it works for me.
My husband and I have our DIY setup in our garage and absolutely love it! I was hesitant to purchase a new Peloton since I had never been the workout-at-home type and was worried this expensive piece of workout equipment would become a dust collector in our garage. We decided to try the DIY workaround before investing a lot of money into the "real" thing.
We use a Sunny B1805 with the Wahoo Cadence sensor attached to the crank arm. I really wanted a magnetic belt drive and this one was probably the most affordable we found. I wish we had spent a little more and invested in a bike that comes with SPD pedals since I know we will be upgrading those in the near future. Other than that the bike is great and I highly recommend it!
We live in CA where the weather is mild pretty much all year so we decided to put the bike in our garage. We screen cast the classes to a TV we have hung up on the wall using an AppleTV and use our phones to view cadence in the Wahoo app. I also have a FitBit Versa that I use for HR purposes, though it does not sync with the Peloton app (huge bummer).
Other odds and ends we have in our setup: WiHoo Mini Handheld Portable Fan we attach to the tablet holder, floor fan, a set of Bowflex SelectTech 552 Adjustable Dumbells for strength classes (we don't do weights on the bike), and a basic Yoga mat.
It has surprised me just how happy I am with this setup! I thought I would feel like I was missing out by not having the leader board and not being able to track my stats. But I have yet to take a live class since the times don't work well for us west coasters with 9-5 jobs and commutes. And while I would like to be able to see output and resistance, I don't feel like my workout is suffering for not having them. I used to take spin classes regularly and most of those were about feel rather than exact numbers.
We've been using this setup since July and, honestly, I don't see myself buying a Peloton now. If anything I may upgrade to a better bike at some point. But for $20 a month I am getting an excellent workout that dips and sways with my schedule. I don't think I could justify being locked into $40 a month when I don't feel I am missing out much on the extras that come with the full price.