ahalpert
Major Contributor
At a 2x squeeze it's absolutely an ultrawide. The vertical won't feel quite as pronounced as it would on a 12.5mm spherical lens, but you're certainly getting that same crazy-wide FoV (and extreme perspective distortion anytime you get close to anything).
Indeed I'd almost argue it's more useful for an extremely wide perspective, as you can get up close to a subject with ultrawide scope lens, and the perspective distortion on your subject's face won't be quite as extreme (giving you a more usable shot) whilst still having the extreme perspective of the wide FoV.
You're getting 12.5mm FOV horizontally, but you'll never get sub-25mm perspective/compression with that lens line.
What you and Postmaster and I are all agreeing on is that - since we shoot portraits - it's great to have a more telephoto rendering of the face to go with a wider FOV.
But by virtue of trading up to a higher focal length perspective all the time, you lose the ability to access that heavy perspectival distortion of the sub-25mm focal lengths - in the (probably) rare situations where you'd want it.