The crop won't or shouldn't distort or affect the aspect ratio but the resize can. Just make sure in the resize that if you type in numbers, only type in only one of height or width and let the other dimension fill out automatically.
Oh I see what I was doing wrong. Ya, this is a great way of cropping photos. I was getting hung up on using the crop tool first. Resizing the width to 1680 and keeping the proportions then using the crop with 1680x153 dimensions worked perfectly. I hope other snapzu users try this tool.