The only reason I use an installer rather than an RBZ is because I have a service that hosts a web app that is used for the HTML interface. So my installer also needs to stop the existing service, delete it, and then create and start the new service.
I put my installer on dropbox and then email the link to my customers. The licensing information is stored in an encrypted SQLite file so it is secure and not affected by updates. Also anyone downloading the the extension only gets a trial until they contact me for a license code. In this way I don’t need to worry about the public being able to download it.
My extension warehouse actually simply points to a dropbox download.