Review on 🔌 CY Ultra Mini DM Micro USB 5-pin OTG Adapter Connector for Cell Phone Tablet, USB Cable, and Flash Disk by Chris Walker

They almost fit in a US dime, they're small. The game controller is recognized via OTG on my LG G4, so they work. You can plug one into a USB peripheral and just leave it there, it shouldn't fall out easily as it fits snugly into the connector. They should work well for small and light peripherals since the connector connects directly to the Android device. I would not recommend using them with heavier accessories or with accessories that can move the OTG port a lot as this could put unnecessary stress on the connector.