Hi Richard,
As already observed, Galerie doesn't have the flexibility of Multigrade. I've found that diffuser enlargers give a flatter result on Grade 2 Galerie as they would on Grade 2-filtered Multigrade, whilst condenser enlargers give about the same result. Galerie is fussier than Multigrade but IMO it's worth the time and trouble, especially if you intend toning the print.
Galerie will tone in selenium to a warm mauve-ish brown colour. Multigrade FB goes the opposite way in selenium, it will turn a subtle cool blue-grey if toned to completion. Multigrade is much more difficult to split-tone in selenium because of the subtlety of the change. With Galerie, the change is easier to notice.
In sodium sulphide, Galerie turns a rich chocolate brown, whilst Multigrade turns a cooler, less rich brown. If you are split-toning, selenium will alter the colour of the sulphide-toned areas to a warm pinkish-brown in Multigrade. On Galerie, selenium seems to cool it down somewhat. I can't tell you what an odourless sepia will do to either.
Selenium will increase the depth of blacks on both papers. IMO, they are both fine papers, and side-by-side you won't see much difference in untoned prints made at the same contrast. But drop them into selenium or sulphide and they are very different.
HTH,
kevs