I use RootsMagic a lot, next to Gramps, because it works well in Linux, under Wine 7, and Ancestral Quest shows some blank windows in Wine, so I need to run that in Windows, in a VM, or by rebooting to Windows 11.
Comparing exports is a lot of work, and since automatic merges are a paid feature in RM, and don’t work in Gramps either, my process is always to export a tree from Gramps, and then let RM look for new information on FS, and that feature is free.
I must add that I don’t use that feature very much, but often just navigate to an existing person to see if there is anything new, and then to a selective download, marking new data that I trust, or adding a few generations to a dead end. Adding many generations in RM is quite slow, so in that case I do switch to Windows for Ancestral Quest. That program also has the advantage that it offers a choice to download normalized place names, so that I get those in English, and not in whatever language that the FS user liked.
Both programs don’t download sources automatically, which is not always nice, so for that the PersonFS Gramplet may be a better idea. There is also an independent Python program that can download large trees from FS, with notes and sources:
This latter program is very fast, even when you try to download 20 generations, and where RM sometimes crashed during such a download, getmyancestors never did. It may be difficult to install in Windows though.
The PersonFS Gramplet is very powerful, I removed it, because I found it a bit too invasive, and because it often missed the fact that a person already exists on FS. And if you add such a person then, other users will be confronted with duplicates, while you will often have no idea about that. RM does a much better check, but takes more time, because you always need to use a GEDCOM file as your transport medium.
So for me, the normal procedure is to use AQ, getmyancestor, or RM to do the FS work, and then import a GEDCOM file from either program into a new tree in Gramps, which I can then check for duplicates, and from which I make a selective export in Gramps XML for inclusion in my main tree.
When I use RM, I often let that search for duplicates before exporting, because there are quite a lot of duplicates on FS, and the RM duplicate finder is very fast and smarter than the one in Gramps. The one in AQ is pretty dumb, so I try to avoid that. I call the one in RM smarter than the one in Gramps, because it recognizes equal dates and places, so that it will never give you duplicate facts or events, unless they are different. Gramps always gives you duplicate events, even if the date and place are the same.
Exports from RM can be a pain if you don’t switch off RM’s extensions, but if you do, the GEDCOM file is pretty clean. The one from AQ is clean too, if you export in PAF format.