Despite initial skepticism that the Cutout Studio could do background removals -- especially complex or cluttered backgrounds -- as well as those I do in Photo-Paint or Photoshop, the tool impressed me. Considering you only have a round brush to work with, the Cutout Studio is quite capable of handling some fairly complex backgrounds. In some cases, a dedicated graphics program with multiple masking tools may be more appropriate (or faster), but Cutout works surprisingly well on a number of different types of images.
I like how it puts multiple views (original with marching ants, tinted view, and transparent view) just a click away. The keep and discard brushes have both preset and custom sizes and between the views, brushes, zoom, and edge settings you can achieve some fairly precise masking even on images with somewhat fuzzy edges between the parts you want to keep and the unwanted background.