The Hori D-pad Joy-Con replaces the left Joy-Con controller on the Switch. It looks more or less identical on the outside to Nintendo’s controller, replacing the four face buttons for a directional pad.
It’s an accessory that makes a lot of sense for the Switch, which doesn’t have a D-pad on the bottom left (unlike almost every other controller, including Nintendo’s own Pro Controller) due to the fact that the undocked Joy-Con controllers need the separate buttons to function as a solo controller.
The Hori controller actually has a few limitations compared to Nintendo’s own: it can apparently only be used in handheld mode, it completely lacks the hidden shoulder buttons from the official Joy-Con controllers, and it doesn’t have an accelerometer, gyro sensor, or vibration features. But the primary reason you’d want this is for better control for handheld play, so those seem like manageable trade-offs.
If those features are truly essential, there is always the option of modding your Switch with a custom D-pad and case (like this one from Basstop), although be warned that the replacement is apparently pretty tricky and will absolutely void your warranty.
According to 4Gamer, the Hori D-pad Joy-Con controller will cost 2,678 yen (roughly $25.36) when it releases in July. There’s no word on any international release.