I use it for "small"ish repos. Mainly I don't want to maintain a copy on disk. I have a list of (and tooling around) what all .debs go in a release, and copy from a master S3 location to the correct apt repo s3 location, and the Packages index gets generated automatically. So I just create a new repo each time but not every .deb changes each time. Other architectural issues kind of drove the need to move to S3, and at that point I wanted to see if I could just keep everything in S3.
Yeah you just sign the packages. There is an option to create a signed "Release" file, but I'm not creating a "Release" file. "Packages" is the only one I'm creating for now. If you wanted to create a signed release file or other files, you could just add that after the step that creates Packages.
True, lambda setup is not super simple. However with deb-s3 you have to have a local copy of the .deb, whereas with what I'm doing the files never leave S3.
Oh cool. The only reason I chose apt-transport-s3 was that it was included in Ubuntu 16.10. It also only uses stuff from the standard python library so there's less bootstrapping before it is usable.
That does look really cool though. For proxies it would be nice if it supported the standard apt-get proxy declaration. Apt-transport-s3 basically does that and sets the proxy env vars.
You could probably get yours into the offical ubuntu repos if you wanted, though.