I'm not familiar with the product you've linked to.
In Mac OS X's Finder you can open a Floating Info Inspector: (Option+Command+I)
Then select a file and this Inspector updates to show info about the selected file(s).
At the top is the "Spotlight" window where you can add metadata so you can search for this file very easily.
If you want to add meta data specifially to Photos, iPhoto is great. Music: iTunes is great, etc.
If the solution above doesn't help, what exactly do you want to achieve (and for what file types)?
Thank you for your help. The metadata added by Spotlight is not written into the file itself, so it isn't what I'm looking for. I know iPhoto and iTunes, but I was wondering if there is a tool that supports editing metadata (that is stored within the file) in multiple formats (pics, music, video, docs, etc.).
I see what you mean... The only time I really need metadata written into a file is when exporting music, which I can do in Logic pretty easily...
I've found this site which might be of interest:
Does this help at all?