Over the years I've briefly played a few Guilds with Muller bridges... For the most part I remember enjoying the basses and don't recall taking note of the bridge much. I'm assuming they do fine if the bass is well-maintained, but in the scenario of one of these basses being a keeper, I would likely end up looking into a replacement bridge since individual string height is not adjustable. Mechanically I guess you could say it has one extra point of adjustment over the old harp bridges, but the rosewood saddles have a whole lot of room for minor woodworking to adjust individual height.
At risk of veering, but in somewhat related discussion, a few years ago my main bass was an Epi Jack Casady signature with the classic 3-point Gibson style bridge. I loved that bass but one thing that did bother me was a string-to-string output/resonance issue; A and D strings sounded noticeably thinner/weaker than E and G. After doing a bunch of tinkering, swapping out strings, etc. I assumed it was a design error with the pickup's flat face (without any adjustable pole pieces) not accommodating the fretboard radius and corresponding arch in the bridge saddles. With the help of some slight compression though, I was able to live with it. However, after a few weeks, I opted to replace the stock bridge with a Hipshot Supertone for the sake of individual adjustment. I never bought the high-mass bridge argument, but noticed immediately that the string-to-string output issues I was experiencing were solved. My conclusion was that, at least on my Casady bass, the 3-point bridge's main points of transfer for string vibrations had to be the two larger outside posts, which are far away from the middle two strings. The Hipshot Supertone is designed so that there is much more contact between bridge and body and it is more evenly distributed. I wonder if I would find myself having similar complaints/suspicions with the Muller bridge if I spent more time with one of these basses...