Resilio is quite the head or two above - very polished commercial product, actually, with basic free license. From the authors of original bittorent protocol and client.

I can't imagine it being "a head or two above". Syncthing has worked flawlessly for me for almost 5 years now.

As far as I looked at Syncthing, it required n^2 config steps for n connected devices. Not really feasible unless every person with access to the folder knows every other person.

...so your use case is sharing your personal folders with strangers without having to authorize them?

Different strokes but a first party iOS client and untrusted remotes are worth at least two heads to me. :)

I have been using Syncthing for a few months now and I love it!