What makes you say that sealed beams are ugly? They're hidden behind the original lense.
https://www.brattons.com/headlight-seal-beam-set.html
How does that work? The sealed bead lense is fluted and the original lense is fluted. Seems the light beam would be, for the lack of a better word, confused??
Another method places the SB behind the original lens, and as you say the double diffraction "confuses" the beam.