Inpainting and img2img masking aren't exactly the same thing, though from an end-user perspective, they both work in a very similar fashion -- you paint a part of an image that you want changed, type in a description and voila! With inpainting, you are limited to a very specific model (stable_diffusion_inpainting, based on SD v2). With img2img mask, you can use any model. Also, due to how resource intensive inpainting is, there are not many workers currently running the stable_diffusion_inpainting model, which has resulted in a ton of issues on ArtBot (error messages saying: "No workers available, try again later."). Things should work much better now! Head on over to the inpainting panel
and try it out!