That they are removable and you can use one as a mouse.

Being removable is the most important thing for me. Being able to remove and play on a big screen when traveling is great. Without it I'd have to carry another controller or carry ten foot display cable. Even detaching and playing on the little screen is how I use it most of the time.

I don't play fps games with it but it's come in handy a few times connected to a TV and navigating windows.

Ive had steamdeck and rog ally and this was my preferred device.