Out of the box I was annoyed at the difficulty in getting the tf2 card slot to work. The included manual is for the sister device, RG353P. Its states (paraphrasing) - hold the power button for 3 seconds to boot into linux.... wut? This device is nothing BUT linux. So I ignored that instruction. Turns out, if you insert a card in the TF2 slot and power on the device normally it doesn't see the TF2 slot. If you hold it for 3 seconds, then it sees it... most of the time. Once I got past that, my next move was to use a better card in the TF1 slot... only problem is, finding the actual FW image online was impossible because Anbernic thinks this stolen linux/batocera clone is theirs. I found one but it didn't work. I tried a cfw, didn't work. What did work was cloning my original Tf1 card image. It took me two tries but I managed it.
Performance - N64 is basically a no-go with the stock firmware. Most games are unplayable. Disappointing. The other disappointment? Pico-8. They've got something really wrong in config files and while I found a fix online, that fix involves rewriting code over SSH and I just can't be bothered when I have other older devices that just work. Dreamcast works great as does PS1 and anything under that as you'd expect.
The screen is..... fine... I guess. It's not a true 4:3 screen so you need to throw a filter on to balance out the pixels. It's also not very bright so if you use the scanlines filter... it's too dark to actually see. "Retro" filter it is then because all of the other choices suck.
The stock firmware isn't terrible but this device could be a lot better with community driven cfw. Anbernic's decision to go closed source is bad for them, the machines they create and the people that love these devices. It's also quite ironic given the stolen nature of their previous devices and software. Because of this, this device is only marginally better than previous efforts. If you can live without Dreamcast, get an older cheaper device that has cfw support like the 351P running Amberelec. If you really want Dremcast I guess you could get this.... or just get something better like an Odin.