I actually have an ST2 antenna and I found it to be directional based on actual testing. One must experiment. Still, my results may or may not be the same as others due to the way it is mounted.
My ST2 is up about 30 feet above the ground. The horizontal mounting bar is about six inches down from the top of the mast. I have an ADS-B vertical omni at the top which positions it behind the upper half of the ST2. The mast sits behind the ST2 for the vertical bottom element. In my testing, I found that the direction the horizontal element was pointing offers improved gain. Hmm...you know I think it may have been directional for me previously when it was the only antenna at the top of the mast, but I really didn't do any testing then to see which direction was better.
Anyways, I also started temporarily using it for receiving APRS and it actually does show directivity of received packets where the horizontal bar is aiming based on the position mapping results. This is based on four or five months of results. I'll aim it in a different direction and report what the results are. Still, I can tell you now that it is directional for me when monitoring steady signals of different power, frequency and distance and turning the mast at and away from those transmitter locations. Others results may vary, but it is incredibly easy to test so have some fun and give it a spin.