GFW-compatible fallbacks are worth worrying about in HK, though, because in normal times there is a massive amount of cross-border travel between HK and SZ. Combine that with grey market HK phones being smuggled onto the mainland to avoid tax, and it's a pretty good bet that any phone destined for HK will makes its way across the border at some point.

If you roam on the mainland with a HK SIM you actually hop the GFW automatically, but most people swap SIMs at the border so that isn't reliable.

This is quite interesting. So GFW is applied by ISPs exclusively on domestic SIMs? Does this mean any international SIMs on roaming hop the GFW?