I have recently bought it in a bundle but haven't played with it yet however as far as I know, it will only export the camera viewports.
But now as I am thinking about it - in LayOut (as you are planning to use it maybe), you can adjust your viewport to any size and when you export the image with transparent background, it's already a piece of cake to select the transparent channel, invert selection and crop to selected area.
OR you can install CubicPanoOut (see in the ruby library depot) and it will adjust your viewport width or height to any set size so you can export easily.
(Or render with Kerkythea or Twilight - I know both can export batch render at given exact size and also a clipmask render to apply in post pro - maybe other renderers can also do it easily.)