If the 1st and 2nd officers of AF447 had understood P+A=Perf. they would certainly be here today.
There were many factors that lead to that disaster. Other than fighter jets very few aircraft are fitted with A.of A meters. A Primary Flight Display (PFD) is able to be overloaded with a lot information including stall information, but can be set by the pilot by selecting the particular phase of flight required; the performance target required is then displayed. This can and does distract from the very simple act of cross reference to the horizon bar and speed. The experienced captain understands this and will always cross reference. However, the captain of AF447 was in bed.
The pilots were anxious and did not want to be flying in the conditions they found themselves. In turbulent sinking air they attempted to maintain altitude by overriding the auto pilot and pulling up which may have been stimulated by the audible warnings "pull up, pull up"; common in many large aircraft when the sink rate is outside certain parameters. A reference to the airspeed would have told them, in the first instance, all was well and at 34,000ft they had plenty of time to think first and then deal with any height loss.
scifi, the purpose of the "flask" is to dampen short term erratic indications. If you have gusty conditions in the house then there is no vario which will be of any use, I would recommend double glazing.