I had to part with my Sei headless 5 when my arthritic fingers struggled with the neck width, I reverted back to 4 strings but couldn’t forget that missing low B.
Salvation appeared when I got my hands on a Wilkinson 4+1 conversion kit and transformed my mongrel P bass, the narrow string width won’t suit everyone, but as I swap between guitar and bass the 16.5mm works for me, together with a regular 4 string neck width, I’m back in heaven