I don't think this counts as "network effect" - I believe that that term applies to situations where the value of the service increases with the (square of?) th

I don't think this counts as "network effect" - I believe that that term applies to situations where the value of the service increases with the (square of?) the number of users. Here, you don't get better insurance as people sign up (at least not directly because people are signing up). I think this is just normal word-of-mouth marketing.