That is the only way to export stills out of FCP unless you use a Screen Capture program like Snapz Pro X. Why would you want to use another method for doing this? It works. The resolution that you get isn't bad. You can set the kind of file it will export to, PSD, TIFF, PNG, etc. It works why not use that?
Well, if your problem is the tedious nature of grabbing a lot of stills, there is one much faster solution I use:
Open a 720x480 Photoshop document;
Open your footage in Quicktime player;
find a frame you want in QT and just drag the image onto photoshop.
Each time you do this, you get a new layer in Photoshop. If you drag it around with the "move" tool it'll kind of snap into place to be properly centered in the image.
If you want to use these pictures for something other than video, resize the photoshop image when you're done (AFTER any necessary de-interlacing!) to 720x534.
Actually, I think the latest photoshop (CS2?) can handle non-square NTSC pixels in a more elegant way, but this should work, and is the only way on older versions.
Anyway, for a large number of still grabs, this can save a lot of time (especially if photoshop is your eventual destination anyway). You can actually drag frames from quicktime onto, say, the desktop, but it puts them in some weird one-frame-movie-clipping format that's not great to deal with.