This service collects your twitter ID and your Mastodon Username and instance domain name. This is then saved in the database providing a link between your Twitter identity and your Mastodon identity. No other information is saved.
When a user logs into Twitodon and downloads the offered CSV file they are receiving a correlated map of Twitter user IDs of user they follow matched against those users' Mastodon username and instance name. If you do not want to be discoverable on Mastodon by users who follow you on twitter then do not login and use this service.
Twitodon does not utilise any analytics or advertising cookies.