I can confirm that the PlayStation Classic is super easy to “hack” using a USB 2.0 flash drive to install the initial payload using controller port 2, then once that’s done, copying everything over to a proper USB drive (in my case a 2TB portable HDD) and plugging it in using an OTG cable. I’m using Project Eris.
It took a little bit of tinkering but I now have the complete NES, SNES, MSX2, Sega Master System, Sega Genesis, Atari 2600/5400/7800, Sega Game Gear, Nintendo GameBoy, Nintendo GameBoy Color, Nintendo GameBoy Advance, and PSX libraries on the drive and most of what I’ve tried works great! I’ve so far finished Final Fantasy I-III on the NES and will be starting up Final Fantasy IV in the next day or two.
As long as you aren’t trying to emulate N64, Dreamcast, Sega Saturn, or newer, the PlayStation Classic is a very solid choice. (Though apparently a couple N64 games do work.)