I have had my Air Boss on Ryan Air a dozen times this year and never been asked about size or weight. Also a couple of times on Easyjet and Air Berlin - same experience.

I don't accept routings through Heathrow, so I cannot comment about the size templates there. I have been through FRA, AMS, CPH, CDG, PRG and a dozen other European Airports on every major and lots of minor carriers and never been asked to put it in a sizer. Prior to the Air Boss, I was asked several times, especially by KL and AF, to show that my 21" rollaboard fitted. It did but for one wheel that stuck out - sometimes they let it go and sometimes they didn't. This was one of the main drivers to look for another solution and research here and elsewhere led me to RedOxx.