I've tried it multiple times, the experience tends to vary. Of course it depends on your personal pain tolerance, but it also depends on the ginger itself. The older it has been in your refrigerator, the more potent it is. Some people even ferment it to increase its potency, though I haven't tried that intentionally yet. I've also heard (and learned) that the smaller the piece of ginger is (naturally, meaning it was harvested early), the stronger it usually burns.
When I first tried figging it was with a relatively large piece of ginger that was fresh, so it was a mild heat kind of experience, it was quite nice and I did enjoy it. There have been times when the ginger would do nothing for me at all, and I'm assuming that this was the ginger itself's fault. There have been other times when the ginger felt unbearable and I would have to do everything in my power to not just take it out.
Today, I tried it again after a while and it was with an old piece of ginger that was as small as a finger, which ended up being a decision I would soon loathe. I scraped it with a fork before inserting it in my bottom, just to get the juices to the surface. I think I left it in for 30, maybe 40, seconds before I rushed to take it out, the burning was unlike any other I felt up until this day. It has now been an hour since I took it out and I can still feel it burning. It was the kind of pain that masochists dream of. As a masochist myself, I will probably end up doing this again with a similar piece of ginger, but with a dominant so that I can't take out the ginger early like I did today. I can only imagine how much more excruciating it would have been if I left it in for more time. I'd imagine it could be used as a punishment reserved for when a sub messes up badly.