It will not lift up if a passenger airbag is fitted. No passenger airbag then it will.
In addition to protecting the passenger in the seat nearest the door it is shaped to protect a passenger travelling in a centre seat of a commercial van. A raised document holder could impair the operation of the air bag in that situation leaving the centre seat passenger unprotected.
It has nothing to do with any activation gubbins being underneath it or anything like that.
This appears to have changed on later models and on my X290 the document holder does raise with a passenger air bag fitted.
I have fitted one to my 2011 x250 although it does have a passenger airbag, now I can have my iPad fitted and running Copilot satnav. I got mine on ebayalthough it is listed as 2014 X290 only. It is a direct fit no worries.