1. Etruscan specialist Larissa Bonfante confirms Etruscan f is a bilabial.
2. Etruscan pairs like pulumχva/fulumχva prove allophony.
3. In allophonic variation, a shared articulation feature (ie. bilabiality) is most economic. An alternation between a bilabial and labiodental sound is comparatively less economic.
4. Instances of Etr f not from allophony are demonstrably recent loans
(cf. Etr fanu vs. Lat fānum, Osc físnam & Umb fesnafe).
5. Bilabial fricative sounds are in no way 'rare'.
6. Several varieties of Spanish use a same bilabial fricative phoneme.
7. Like Etruscan, Yimas shows increased sonority of /p/ before /u/ & /w/.
8. It's not absolutely certain that the /f/ of neighbouring Latin was strictly labiodental.