I have a GPD Win 3 and I've been enjoying it. The Steam Deck is interesting for the larger screen and cheaper price. The ergonomics of the Win 3 make my hands cramp a bit after long sessions so I think the bigger size and screen will be welcome additions. Steam Deck's price looks awesome. Some comments have been made about the storage size and reminder than there is a microSD slot. Although I would agree that the base storage size would still be good to upgrade.
I'm kind of looking forward to seeing what an Arch linux based OS customized for Steam look like.
Looks more adult/teenager hand designed to me. https://youtu.be/oLtiRGTZvGM