The FAQ is extremely unclear, but if I'm understanding it right, doesn't this make transfer out to Internet significantly cheaper if you insist on using AWS? Instead of paying $0.09/GB, transfer to Lightsail for $0.02/GB then transfer out for $5/1000 GB=$0.005/GB. You do have to deal with changing IP, but you get a 1.26 order of magnitude decrease in price, and that's assuming you don't bother actually using the extra compute.
No, unless you setup VPC peering between the shadow lightsail VPC and your AWS VPC, otherwise you'll be charged at least the $0.01/GB on egress, and maybe the $0.01/GB on ingress into lightsail too (not sure, the wording makes it ambiguous, one would have to try it.)
