This is my first retro handheld and I have to say that it's fantastic. I wanted something extremely pocketable and it's perfect for that. The RG280M feels great in the hand with its premium-feeling metal body. I was also impressed that the screen looks good from all angles--considering that I used to own a Gameboy and a Game Gear back in the day, it is mind-blowing how such a small screen looks light years better than those devices did.
About the only thing that could've been approved is the stock OS experience--it's a little dated, feeling like that of a mid-00's cell phone, but it gets the job done, and once you're in an emulator you don't even notice. If you're looking for a device that is more at the extremely small end of portability, this is it. I have a Steam Deck as well, and the size difference between the two is substantial. I find myself using this one a lot more simply because it's way, way more portable.
If this review is any indication, I played the RG280M for a week and was impressed enough that I followed it up by ordering an RG405M so that I can cover my bases in terms of portability size.