Ok, so today I received the Declaration B3 brush in custom handle and did three test lathers. For the first two I hand lathered and then face lathered some Stirling. Wow, this is a dense knot! Now please note, I'm a badger noob and haven't had the pleasure of owning a Simpson Chubby or one of the Shavemac, but the density of the hairs truly surprised me. I believe it's at least twice as dense as the Stirling finest, my SWMBO confirmed. Here's a picture comparing the two, towel dried:
The brush absorbs crazy amount of water but is not overly soap hungry and loading is surprisingly easy. The brush felt very nice on the face, the backbone is perfect imo, any stiffer and it would be uncomfortable. Compared to Stirling, the splay is much more controlled. There is a noticeable amount of scrub and according to other reviews, it's here to stay for a dozen or so uses.
Awaiting next shave to see the true performance of this beautiful bruhs. Also, I have a 30 mm finest Maseto incoming and will update my impressions.
Here are some more pictures: