From the website:
Topaz ReMask is specifically engineered to supercharge the masking and extraction workflow for photographers and designers within Photoshop. Other masking tools - both within Photoshop and other third party filters - require intricate brushing, sampling, and refining for a detailed mask. Topaz ReMask, on the other hand, does all the heavy lifting while requiring a minimum of user input.
I bought this a few months ago specifically for my modelling photo's. I like to add custom backdrops, even if it's a plain white backdrop.
the software is phenomenal. It's extremely easy. You basically draw a brush stroke (as thick as you want) around the edge you want cut out. Then fill in the bit to keep in green and the bit to go in red and that's it. it really is that easy.
There's a demo for download, but if like me you like custom backdrops...this is for you.