This was a really well-made and designed product. I'm using the triple controller to play arcade and 16-bit games on my PC. Also, I can't notice any input delay when using the controller and all three controllers show up as separate devices which is cool. Not sure if you can use multiple ports at once though. Lastly, this is such a great value other competing devices cost 2-3x this price and only allow one controller type to be used.
Here are a few tips I think could be helpful. I'm using an Arduino pro micro clone from AliExpress and found that the Sparkfun Arduino 5v pro micro drivers work great with the clone. I also tested the controller using gamepad-tester.com and it shows that down and right are being pressed. I thought something was broken or I had done something wrong but it actually works fine, not sure why the gamepad-tester is giving those readings.