We bought this product ... Peerless-AV SR598. We have had very good experiences with it. However, it should be noted that the height is not variable (the locking screws have to be loosened and tightened to a new height - 2 to 3 people required > two lift the screen, one screws it down).

Too large for a mobile frame

None: moving the screen endangers its integrity. Risk of contact when passing through doors...