It'll be interesting to see how it fairs against the Steam Deck. Given the option, I'd still take the Deck hands down because Linux + Valve customer support. I would dread the moment I have to try and contact Asus support.
Now is the time for Valve to release the Arch based SteamOS 3.0 officially so that it can be easily installed on non-SteamDeck hardware.
Proton was the missing piece that makes Steam Machines viable. Valve should be making SteamOS 3.0 available to hardware companies like ASUS. The Ally should have been a SteamOS device, IMO.
It's not up to Valve. GPD Win4 is an amazing little device with slide out keyboard 32 GB Ram and LTE that runs SteamOS. It's much faster than my current laptop and would make a fine replacement.
ASUS is getting a little bit better with their Linux support, but Zenfones for example were great little devices with atrocious software support.
SteamOS 3.0 (what runs on the steam deck) is very different from the SteamOS that they've been releasing for a while now. and, unfortunately, 3.0 only runs on the steam deck right now.
I tried it out on my GPD Win Max 2 and it ran great, until an update borked it. That was a while ago, though, so I assume things have only improved.