The only issue I have with the 80 vs 100 point thing is that neither result is favourable for the new player.
If the newbie wins, you can just say it was because of the points handicap.
If the newbie loses, it's more embarrassing that you lost to 80 points.
I guess it comes down to personality and who you're teaching. Personally, I didn't want opponents to hold back when I started and it was a great learning experience even when I lost horribly.