ECHZOVE Keyboard and Mouse Adapter for Nintendo Switch – Compatible with PS4, Xbox One, PS3, Xbox 360 – Plug and Play USB Gaming Converter with Custom Key Mapping, No Lag Performance for Players

I bought this primarily for playing rhythm games on the Switch, such as Taiko no Tatsujin and Muse Dash with a keyboard. And I can say it works great for this use case! (Can't speak for how well the mouse controls work, since I haven't touched that).

Connecting it to the Switch is pretty straightforward. Only point worth noting is that it seems to require more power draw, so you'll need to plug it into the USB port on the back of the Switch dock rather than the ports on the side. (This is also mentioned in the tutorial video).

Setting up the button mapping is also pretty straightforward following the instructions in their tutorial video. Just hit F11+F12 to enter mapping mode, and plug in a Pro Controller into the middle slot. From there, you just hold down on the pro controller button you want to map, and press the key on the keyboard you want to map it to.

As far as lag goes...
I have Muse Dash for both Switch and PC, so this was a useful reference point.
I tested it out both in docked mode and in handheld mode using a USB adapter.
There was absolutely no noticeable lag in handheld mode. I did notice a bit of lag while playing in docked mode, but I'm guessing this was due to my display rather than the adapter itself. (Worth noting that this is a common issue and most rhythm games have calibration modes to adjust for display lag, and that I've also noticed similar lag when trying to use a wired fightstick for rhythm games. ).

Tried a random adapter that was cheaper didn’t work just buy this one!! Don’t waste your time with the cheap stuff!

The device works as expected in Switch and PS4.... I wanna try it out on my PS5... While most people don't like to play with a keyboard... I find some games in the console easier to play with it... I gave it a try and it performed as expected... There's one thing to notice and is that there's a minimum delay when you press the key and the input received in the game, I didn't find it troublesome but I bet some people will... Is a little hard to set up so I had to read carefully the manual to understand the custom setup phase (I like to play with a specific configuration)... Apart from it... great purchase

My son picked this out so that he could connect his keyboard and mouse to his switch. He says it is perfect and loves it. Seems to be durable and works perfectly. He has loved being able to play his games like his is on a computer and it has allowed him to play some of the games he plays better (according to him). He says he would recommend it to a friend and purchase again.

Item was exactly what I expected it to be. Very straightforward. I wish there was a key to the keyboard layout, but it wasn't hard to get the rhythm.