Dicor lap sealant or Eternabond tape for new roof vent

I should have looked at the fan before I asked this question, I assumed it would have a nice wide flange like the fan it replaced, but it has a plastic flange (narrower at the front) with a couple of projections on each side of the flange that extend to the edge of the flange. So instead of a nice uninterrupted segment of Eternabond tape, I'd end up with notches in it that I'd have to cover well with Dicor anyway.

So, I just used the Dicor and didn't bother with the tape.

Thanks everyone for your advice!