No third-party application should need your Frontier ID, especially not in connection with your IP address. MetaElite collects both.
The Privacy section on Raxxla.org states that the MetaElite app "requires your credentials (FID + AuthKey) for access: It stores your FID, Cmdr Name, and the AuthKey hash.
Only Frontier should ever need your FID. EDDiscovery, ED Market Connector and SRV Survey use API keys to connect players with their accounts on third-party websites like Inara and the Elite Dangerous Star Map. They also use Frontier's Companion API, which reroutes players to Frontier servers for login. Neither of these gives the third-party apps direct access to your FID.
MetaElite does none of this. Moreover, the application stores data on a backend server, but because the software isn't open-source, no one but the developer knows what data is stored.
Simply put, this is a privacy violation waiting to happen. Multiple players got doxxed a few years back when the creators of EDRecon used data from that app in violation of Frontier's Terms of Service, and while I doubt MetaElite's developers have the same intentions in mind, they shouldn't be asking for players' FIDs in the first place.