Mlem dev here. Mlem currently supports two PieFed-exclusive features:
- Polls: see !polls@piefed.social for examples.
- Adding notes to users: click on the menu in the top right of a user profile and choose “edit note”.
PieFed has many more features that we don’t support yet (see Rimu’s message). We do not yet support crosspost merging.
The most feature-complete experience on mobile would be to use the PieFed website directly. There’s a detailed comparison of different apps’ support for PieFed features here: https://piefed.social/community/fediverse/wiki/piefed-app