Dunno if anyone still checks this thread but I got a second Hori Pad controller for PS4 and what I thought was a defect seems to be an actual flaw of the controller.
The L2 / R2 buttons are very pressure sensitive. I've done several tests in games where you need to hold L2 to aim or R2 to drive. If you don't push hard enough, the game stops aiming or the car you're driving slows down.
Now, I'm not trying to badmouth this controller. I love everything about it except for this issue. Considering I can't find much about this problem, I'm going to assume other people press it harder than me. But I have found that I can actually make the L2/R2 buttons "click" without the game registering it. If you use just enough pressure to make the click feel, but not enough force to press the button at your hardest, it will not register the press. I've tried this with both controllers.
My issue is in games where you need to hold L2/R2 a lot (aiming in FPS games and driving in race games) this controller is basically useless to me. I think it's because I subconsciously use less pressure after a while. This isn't an issue with the original DS4 controller because it register the button press much sooner than the Hori Pad does. I feel like I really have to keep pressing the Hori Pad L2/R2 hard for it to stay working.
This flaw isn't as noticeable if you just have to click L2 or R2, but once you need to hold the buttons, it starts to show.
If Hori managed to fix/improve this, it would be a perfect controller for me.
