As many other apps, Lineage Downloader is affected by the problem of Android Piracy.
This means you can the find the Premium version online and access to all its features without paying a cent BUT it’s really worth saving 2$/2€ and risk to download an OS from untrusted sources?
Lineage Downloader server downloads LineageOS builds verifyng their authenticity and integrity and produces the necessary Delta updates for all its users. The same process is done on the app assuring that you download the exact builds that LineageOS team publishes.
Would you imagine what could happen if you use the pirated version? In this you could download a system update containing malwares that could, for example, collect and send all your sensitive data to unknown servers/people.
So, for the security and for the privacy of your data, you should download Lineage Downloader from Google Play, the only channel on which I release it.