Sorry I misunderstood you earlier, i thought you meant replace typical center speakers with constant directivity speakers.That's not really a broadband directivity speaker. Besides it is type of horn speaker (waveguide=short horn profile). Anyway, that's a different topic and doesn't belong here.
My point is that using a center speaker with a directivity as poor as this, and which is the case with many center speakers, generally isn't necessarily better than dropping the center speaker all together. But in order for the image to be stable with only two front speakers, it's important with a uniform beamwidth and avoid early arriving reflections.