^ "Knife-edge" seems to be a generic term with two connotations:
A) arms moves up/down on a sharp blade; it moves easily with minimal resistance and it’s great in that respect; basically, it replaced Uni-Pivot with a straight line, keeping the low resistance but adding horizontal stability.
And B) they’re not very good.
So "knife-edge" as a concept has a bad reputation.
But not all knife-edge bearings are the same. The knife-edge bearings used by SME and SAEC are very different and can’t really be compared. Just looking at the bearings on their on shows extreme difference, not just in appearance but in action. SAEC’s "double" knife edge is genius, once you understand how it works. The rest of the SAEC arm I worked on wasn’t even close to the high standard of its bearing.
Jelco has introduced a new knife-edge design. I’ve only seen good, detailed close-up photos, but it’s radically different than either SME/SAEC and looks brilliant. SME’s design, from 60 years ago, is the simplest and has the most "slop". Later improvements by other were total departures from the primitive SME design, and eliminated slop.