Layers is a great new tool. For years I've had to Photoshop screenshots to extract the various elements (windows, menus, menu bar icons, desktop icons), it's so nice to have them in individual layers.
IMHO this does not replace SnapZ Pro, it complements it. SnapZ Pro is better when you just want a selected area or need a movie.
My only criticism is the default keystrokes which use the shift-option combo interfere with valid characters. I quickly changed them, that process was easy & worked AOK.
Other minor gripe: The Buy Now link to me to PayPal's Spanish site, there was no obvious way to change the language to English. I have a PayPal account, so once I logged in it was easy to figure out.
Kudos to the developer: this tool is a must-have for me, I write a lot of user docs & help & am always grabbing stuff off the screen.