Fietsbob, thanks for the reply.
I've probably read every post and comment on Jan Heine's "Off the Beaten Path" blog and frequently visit the Compass / René Herse website. I've also read many editions of Heine & René Herse cycles' Bicycle Quarterly. As you might expect, there is little or no critical feedback about Herse components in any of these. I don't recall reading any comments at all about the performance of Herse brakes. Fair enough, I don't expect to see critical comments in any advertising.
I have read, in Heine's blog and elsewhere, many comments admiring the look & quality of the brakes. I've also seen many photos of "randonneuring" bikes equipped with these brakes. I even saw a couple of such bikes at LEL in 2017, but I didn't speak to the owners. Centre pull brakes with brazed mounting posts are generally on bikes modeled on French low-trail, brevet bikes from the 1940s–70s. I like the handling of low-trail bikes, but I'm not interested in replication for replication's sake. I want to know how well these brakes work before I pay the not inconsiderable price for them! I'm sure they have good points and bad points. I want to know what they are.
I'm aware of Paul centre pulls. They don't mount to the same type of braze on post as Herse centre pulls and are CNC machined rather than forged like the Herse brakes. I think they may have less reach, I haven't checked them for some time. Like the other brands of centre pulls I mentioned, they are similar to the Herse brakes but … different. The Herse brakes are based on MAFAC Raids but supposedly improved in many ways (shape of the arms, stiffness, bushings, springs &c). Nevertheless, information about MAFAC Raids or other models may be relevant.
I've heard a little about post splay, too, though I'm not 100% sure if it was about Herse brakes or other brands. In Off the Beaten Path Heine says that cantilever brake posts can twist the forks but centre pull posts don't because they're mounted higher & closer to the fork crown. This makes sense to me, but I don't know if it's true. I intend to use a Herse rack that mounts to the brake posts which may minimise any splaying. I don't know about that either, so I'm also interested in hearing from anyone who's used the brakes with the rack.
Thanks again.