This app is a nice addition to Quick Look, but still has a few idiosyncrasies to work out. It provides a clean way to see EXIF and other info with quick look, and had no problem with image files from my Canon point and shoot, as well as my Nikon D90 (with RAW files).
The loupe function is a bit odd, and that's where I have my issues. First, it can be active all the time, inactive all the time, or triggered with the caps lock key. Unfortunately, I found the loupe difficult to trigger with caps lock key. It worked for my NEF (Nikon Raw) files, but not consistently with the jpeg copies of those files, or JPEG originals from my point and shoot. It seems you have to click on caps lock, then choose or scroll to the image; you can't have it selected already.
I would suggest making the loupe pop up in the window if you hold down a modifier key (like option or control?), or at least turn on while you have the preview window open with the caps lock key.
My other comment is about support and feedback for the developer and the product site. The in-app info box says to go to the website for info and tips. There is minimal info, and no real tips that I can see. Furthermore, there is no clear way to send feedback to the developer via the app or the website. This is a must, particularly for a product that needs some work still.
Looking forward to seeing future versions.