Thanks for those tips. Someday it might come in handy.

Last time I was at KUL they were still using LCCT. The tiny warehouse with no jetbridge. AAX was just a new thing and no fly-thru likes nowadays. So can't really comment on KLIA2 but heard it was well designed. Even the old LCCT is lightyears better than 2nd tier airport Ryanair serves, BVA comes to mind immediately.
Used Optiontown once to try score a lie-flat from crazy sale fare and didn't get it so I don't know how effective to score upgrades back then or these days.