I think BL means that any of the stereo pedals can be used as a stereo Seraphim or any of the other stereo pedals. Since the Seraphim is hard to find, just get the cheapest v2 Neunaber stereo pedal (you can find them $200ish on reverb) and download the software.
The series of pedals all have the same guts. The only difference is what they come preloaded with, and how the pedals are labeled. It's a cool concept, but how they implemented it is a little confusing.
I have the stereo Expanse. With a USB cable and the software, I can get all the sounds and functionality of the Seraphim. As well as the other expanse series.
Hopefully I didn't make this even more confusing.
From their site:
Expanse Software Expanse Software can transform your v1/v2 Stereo Effect pedal with USB jack into any available effect. These pedals include:
Have a mono Seriphm mine is the V2. It replaced a Strymon Blue Sky on my main board but I don't run Stereo. Why not just grab a Stereo Immerse new? You can get more than just the Shimmer and those are killers. https://neunaber.net/collections/all.../immerse-mk-ii