Filter+ was an Isotammi addon for 5.x Gramps.
It features a Define filter scraper that saves the current Filter parameters into a Custom Filter and integrates a timer feedback.
Filter+ was so useful that it was rolled into the Gramps 6.0 core as a replacement for the original Filter gramplets.
Also, his experimental cancelable Filter progress dialog is very useful for 5.x
And the recent 1.2.7 update of FilterParams simplifies saving or sharing custom filter definitions.