That dude left out a couple negatives.

First, all games will default to the Deck's output resolution. You need to go to the game's settings before launching to set the resolution to match the TV's.

Since running a game at a higher resolution hurts performance, you'll usually get worse performance docked than handheld unless you're ok with using a lower resolution intentionally.

There are various issues with external controllers. Here are a few that I've had personally:

1. PS5 controller developing input lag over the course of an hour. Need to disconnect and reconnect.

2. Double inputs caused by Steam Input happening on top of a game's built-in input

3. Some games not correctly interpreting multiple controllers because the Deck's controls still register as a controller while docked

4. Some games like Stardew Valley not accepting controller input without going into settings and reordering

5. Not reconnecting to Bluetooth controllers automatically, needing to go to settings and manually connect (for some reason this doesn't happen with Xbox controllers for me)

Unrelated to controllers, there are some other dock issues:

1. Constant audio buzzing and disconnect while docked. Need to enable Developer mode and change a setting to fix.

2. Severe UI slowdown while docked.

These are all with the official Steam dock. So yeah, it's not the seamless Switch-like experience a lot of Deck users pretend it is.