Jay Jay,
Yeah, I've used Parafilm on canopies. I usually use it on bubble canopies, like the ones found on modern jets and WW2 fighters. It takes some practice to get the hang of it, but it works well for masking. Like you said, one of the nice things about using it is that it's pretty clear and easy to see through. Another is that it cuts nicely when you use a nice new Xacto blade. Like I said, I use it on bubble canopies, but for "panes," I still use tape to outline the frames with masking fluid covering the rest.
Parafilm is pretty cheap for a roll, considering how long a roll should last you. I remember paying around $10-12 for mine, and it lasted several years. It wouldn't hurt to invest in some. Play with it on your canopies. If you don't like it, you can always use it for camo masking.
Cheers!
-O