We’ll write the conclusion first: In our opinion vortex generators (VGs) are so effective in reducing stall speed in virtually all stock general aviation singles, and Vmc in twins, that we think installing them significantly increases the level of safety. While we have never ranked add-on safety devices for airplanes other than to say shoulder harnesses are number one, we think VGs could arguably be number two.
When things go south and you have to park an airplane in an unintended location, touching down at a lower stall speed means less energy to dissipate in the crash. Energy is a squared function, so reducing impact speed, even a little, pays big dividends. In a twin, reducing Vmc means reducing the risk of an uncontrolled roll following engine failure. A crash right side up means a far higher chance of survival than smacking the ground inverted.