Well done. It works a charm so far.
I made two refreshable groups before doing the 9.1.0 update in my database of about 42,000 people. One group was Birth => Date => Is Blank. The other group was Birth => Date => Is Not Blank. I don’t think it matters whether the group is refreshable or not when it comes to the time to apply the group as a filter, but I made these groups refreshable.
Before the update, it took about 15 seconds to filter by either group. It didn’t matter if I was switching from no filter to filtering by the group, or if I was switching between filtering by the two groups. It didn’t matter if I was applying the filter in People List View or in the Index tab of the left sidebar
After the update, the time to apply the filter can’t be measured by hand because it’s too short. It may be a half second or a second or something like that. So it’s not instantaneous, but it’s still quite user friendly.