When Sync for Reddit show a popup promoting Sync for Lemmy, it should also point to this kind of service, to ease the migration. It would also be nice, if sync for Lemmy also had a shortcut.
Besides that a link to a more general community directory like https://lemmyverse.net/ would be nice to have.
Sync is a for profit app. Why would the dev not have the right to advertise the one other app he is developing? And in order for the user to become interested, he has to sell the idea of Lemmy first if we are talking about new users. If we talk about old Lemmy users, then he should be advertising his app on Lemmy itself which he is already doing by setting up a community and posting to other relevant ones.