I'm expecting both systems transmit well under 50 MB/month. They use fundamentally alike premises. Find My also literally takes over a slice of your wifi & share info on gobs of devices it sees. That there is less user interaction with Find My does not make me- like it seems to make you- feel much better about the situation. But it also ought be a relatively negligible amount of throughput
Alas, as usual, these cloud-run devices seem to offer no visibility, no way to see or understand what devices we "own" are doing, gives us no grasp on how they are behaving.
There isn't a qualitative difference between the two in my view (there might be a quantitative one – Sidewalk's data cap is 80 kbit/s or 500 MB per month; Apple isn't publishing this data, but I'd expect it to be lower, although not limited to wi-fi and also using battery power).
The maximum bandwidth of a Sidewalk Bridge to the Sidewalk server is 80Kbps, which is about 1/40th of the bandwidth used to stream a typical high definition video. Today, when you share your Bridge’s connection with Sidewalk, total monthly data used by Sidewalk, per account, is capped at 500MB, which is equivalent to streaming about 10 minutes of high definition video