Got the RP5 today and some accessories. My impressions are mainly versus the Razer Edge, which is pretty much on par with it spec-wise. The Edge has a better CPU, but the RP5 has more RAM.
-The RP5 feels pretty comfortable to use and somewhat pocketable, but I'd rather put it in a case. Speaking of which, the official Retroid case is good and provides adequate protection, plus space for the USB cable and charging brick. The official charger is 35w and is one of the slim GaN types. It can handle rapid charging.
-While there's no comparing the power of the RP5 versus the Trimui Smart Pro, I still like the Smart Pro a lot and I think it's also more comfortable. I'm gonna keep using it for lower-end stuff and Portmaster.
-The screen on the RP5 is fucking gorgeous. Nice and vibrant- what you'd expect from an OLED screen. But I think the Razer Edge's screen is more impressive, especially since it's 144hz. The RP5 is only 60hz, although for emulation this really doesn't matter.
-The speakers are also great and can get loud enough, but once again the Edge wins out here- it has louder speakers.
-The RP5 wins where it counts- with its controls. They feel better and are quieter than the phone controllers I've tried with the Edge. It's also smaller and more travel-friendly in comparison. Plus it has a more recent version of Android, so some games that won't work on the Edge work on the RP5.
-I need to test video-out. The Edge can do 4K while the RP5 does 1080P. However, I have constantly run into problems with video-out on the Edge (either it doesn't work or will work, but not charge at the same time) and I'm hoping it will be much easier with the RP5. One thing I also like is that there's a setting to allow the screen to be off while using it on a TV. You can't do that with the Edge and you have to download an app to make the screen black as a workaround. Video-out has been the only real big negative about the Razer Edge, so this could be a big deal for me if the RP5 works smoothly.
Is the RP5 the best Android handheld out right now (in its price range)? Yes. Would I recommend it? Yes, but only if you want really good higher-end emulation for PSP, PS2, GC, 3DS, etc. I have yet to try Switch or Wii U so can't comment on those. Would I recommend it over the Razer Edge? Yes, because of the later version of Android, better controls (compared to the Kishi v2 Pro and Backbone controllers at least), and seemingly hassle-free video-out. If you just want to play 8-bit, 16-bit, and PS1, get a Miyoo Mini or Miyoo Mini Plus. If you want that level of power but with some PSP, Saturn, N64, and Dreamcast also being playable plus Portmaster, Then I'd recommend the Trimui handhelds.