edns-client-subnet leads to a surprising number of privacy concerns. See:
https://00f.net/2013/08/07/edns-client-subnet/ I find the cache timing issue particularly worrying.
Cloudflare runs from 151 (and growing rapidly) locations worldwide. Without edns-client-subnet, the upstream DNS server will probably respond according to the geolocation of the Cloudflare location you're talking to -- which is probably pretty close to you, and therefore will probably produce a good outcome for you, while largely avoiding the privacy concerns.