Steam Deck

Benefits:

• Changes are persistent. Unlike SteamOS, which uses an A/B partition scheme for upgrades, every update is a new system image but leaves your home directories alone, and you can easily rollback or rebase at will without much issue.
• Several built in tweak commands to set up or modify different settings/apps.
• Comes with many QoL bundled apps.
• Can utilize Distrobox to install other software from other distros.
• Active and responsive devs and community.
• Works on both desktop and handheld hardware.

Drawbacks:

• Does not always get updates as quickly as SteamOS (it's nearly bleeding edge, but not quite).
• The fully Atomic nature has a learning curve, and system management may be challenging, depending on what kinds of tweaks a user intends.

There may be other technical aspects that differ, like battery life, but I don't know enough to say if they are different in practice. Fwiw, I have Bazzite on a laptop and SteamOS on my Deck.

Main benefit for me is a more traditional Linux environment, whereas steamos basically has a single user without a password and encryption is difficult at best. Great for playing games but not for computer usability. Bazzite also supports full disk encryption, and recently I learned/was told that you can move your SD card between Bazzite devices like Nintendo cartridges to play wherever.

One downside would be arguably less support. It's community driven so the hardware manufacturers aren't going to necessarily help you get dysfunctional games working, etc. Not that they're going to be much help even when you're playing native.