I recently bought a 4" 27-3 that was a B&D conversion.
For me it was a matter of wanting the rare 4" 27, but the pistol had the conversion and second cylinder.
I found a new 27-3 side plate to replace the B&D marked plate and keep the B&D side plate and cylinder in a safe place.
I have no interest in selling the cylinder and side plate and I have no interest in using them either as IMO the cartridge is tough on the revolver top strap.
If I want more power I can use a 44, no need to hotrod the 357.
I do value the conversion as a historical thing.