Now for what I don't like. the extender goes on the camera very solidly. I haven't had any problems with it moving. However, the eyepiece itself fits on the extender loosely. I mean, it is very easy to move the eyepiece off the extender, just by applying any upward force to the eyepiece. I would imagine some silicon caulking (just a dab) or some other easy to remove glue would fix this annoying problem.
I had the same problem with the original eye cup fitting loose on my 300D. I up graded to the 20D about a year ago and use the same extender on my 20D, but the original 20 eyecup fits very snug. I couldn't tell you for sure if all 20D eyecups will fit snug, but might be worth a try to pick up a replacement 20D eyecup and try it out.
Like you I really like being able to see everything with my glasses on and the image being smaller is no problem.