Broadcasting the secondary SSID by itself has no significant impact but there is a wireless performance penalty to having lots of nearby devices connecting (by

Broadcasting the secondary SSID by itself has no significant impact but there is a wireless performance penalty to having lots of nearby devices connecting (by default) to open networks especially on single radio/band devices. If I lived in an apartment building or near a public space like a coffee shop / etc I would opt-out. On the security front I don't think it's much of a concern. These community wifi services have been widely deployed to millions of devices around the world and enterprise wireless APs have offered similar features for many years. There's always some risk but nothing extraordinary.