Airspeed indicator has inherent flaws, and the AoA gauges fix one of them. For short field landings, the AoA gauge will be much better for your performance and safety margins than your AS gauge. It doesn't matter the DA, the weight or the bank angle. It's always right.
https://www.ntsb.gov/safety/mwl/Pages/mwl7_2015.aspx
Costs are coming down for GA. But, as good as they are, if you're a crappy pilot, another gauge ain't gonna help you.