I use them constantly. And I modify their proportions for my characters body shapes. The handiest thing is that you can find tons of poses to drag and drop onto them, or you can use the image capture feature to pose them from a photo.
And of course I can find 3D models for anything else I need, like animals or buildings. The asset store has plenty of variety.
There's a bit of a learning curve, yes. But once you get the hang of it, it's not that bad.