I think that precut Kabuki-Tape masks are excellent, but I never buy them, I only use them if they are supplied with the kit. It seams that many modellers find masking canopies one of the worst jobs when building model aircraft. This is understandable, as you don't find out if you have been successful until near the end of the build when you can finally take off the masking. If it hasn't worked well you may have ruined the model or at least caused youself more work. I've been there, so I know it aint a good thing
Kabuki tape is good because it doesn't leave a residue, I use Parafilm-M for the same reason. However Parafilm-M requires more effort to use effectively, again I have made the mistakes to know.
I was recently asked if I could make canopy masks for a 1/24 scale Bf 109 with my "miracle Paint Masks" (see side bar ad). I could but I would need to have the actual canopy to make masks to fit, but I don't have the kit. (look for Trev (ruby6990) ) because, of course I directed him here. I explained to him how to use Tamiya tape by cutting into thin strips, but It would be best if I were to show some pics. I thought I had some and I said that I would show Trev but either I haven't or I can't find them. I always intended to do an article on masking canopies, so maybe I should. In the meantime I will try and get a couple of pics to show the technique using Tamiya tape. A picture paints a thousand words.