First of all, the app is open source: https://github.com/mtotschnig/MyExpenses. In addition, the apps available in the official F-Droid repo are subject to regulations. And with the app there is no hint, with undesirable features. In addition, the app is also built again by the F-Droid team and if something is noticeable there, the building is interrupted.
I can recommend the app in my experience. I also purchased a license. It will connect to licencedb.myexpenses.mobi and validate the license. After that, you can block the app traffic with a DNS filter app (personalDNSfilter, RethinkDNS, etc.). At least that's what I did.
If you still have concerns, you can contact the developers at Mastodon (@myexpenses@mastodon.social).