I was doing a little online window shopping -- Briggs makes a 21" expander that looks really nice. I know that for LHR I can't use the expander, but for other travel it's great. Here's the link:
http://www.briggsandriley.com/travel...leupright.asp#
Do you think this would be as safe as the plain-jane 20"?
IMHO it looks very tight and could well be challenged by the BAA enforcers! As said above once you are stopped they dont give up! I would stick with the 20" - I have both 20 and 22" and when going through LHR always take the 20" and even then have had to prove that it fits within the guide.