Outside of cosmetic, the main difference was the extended fretboard on the 39. If I was more into strumming, I would have kept it, but I find the extra frets on a soprano get in the way of my finger picking.
Interesting that Sven-uke says his SK-28 isn't loud. My SK-38 is super loud for a soprano. Just as loud as my KoAloha Opio soprano. The SK-28 looks like it has a narrower body though, which could affect sound. I haven't seen an SK-28 IRL so just judging by photos, but my impression was that the Nunes style has quite narrow bouts.