The decision over whether or not a bot comments on posts it votes is up to the bot owner. I've considered removing the comment from @postpromoter but it provides significant visibility to the service and to myself. Additionally some people like the messages as a sort of disclosure that the post has received a paid upvote.

So for the time being I intend to continue having the bot comment on posts it votes, but there are some other bots, like @buildawhale, that don't leave a comment as far as I am aware.

Thank you for your support!