I started with a RG35xx which was/is great but then wanted something more powerful.
I almost pulled the trigger on an RP3+, then a 405M but didnt and went for a Steam Deck.
So glad I did, its plays just about everything I've thrown at it including Xbox 360 and PS3. The big plus points though are;
The overall usability - SteamOS really makes it
Valve support - They have been fantastic and answered all my queries. I had a minor issue, they sent me a brand new Steam Deck under RMA even thought I bought it second hand from these forums
Trackpads and many buttons - easy to configure controls for games and systems
The sheer amount of people that have one, finding help is easy.
Proton - Allows you to play games that simply dont work on modern Windows and are too slow for PCem. Games like Motocross Madness 2