I used 'normal' notation for years before I started shape note singing, and it took a little while to adapt (in the sense of being able to 'sing the shapes' at the speed of experienced singers) but I do find them helpful - in fact, if I'm struggling to sight-sing something now, I mentally convert it into the shapes, which always seems to solve the problem.

I think this is partly for the speculative reasons above (eg that it no longer matters what key the piece is in), and partly because there's a very simple, direct link between the visual and the audio.

Yes, shape notes were created as a pedagogical tool, but they're also a very quick way to get a lot of people singing a new piece together, without needing to play through or teach each part separately.