Posting about another great Raspberry Pi product, the PiBoy DMG: 
https://www.experimentalpi.com/PiBoy-DMG--Full-Kit_p_18.html
(Info from their website at the end of this post...)
Its really flipping nice. The additional boards that are used for the LCD  screen, the controllers buttons and the built-in fan are quality and well  engineered. Its a tight fit with a Raspberry Pi 4, but it goes in... and runs  between 45-60degrees at a high load. You can overclock, although I stay on the  light side at >2000mhz so temps remain in the range posted. Experimental Pi is  the company producing it and they supply a specific (albiet one version under  current) RetroPie OS image. Also, you have to install the 'Firmware' which is  really just the LCD drivers, a safe shutdown script so the gameboy power button 
can be used (It's one of the nicer shutdown routines I've seen, too. Some for  the Pi, like the NESPi 4 NES case w/ SSD Carts, do close open apps but do it  less clean than on the PiBoy DMG.) and a volume button screen overlay... twist  the volume button, and a nice overlay like on an iPhone pops up.
Of course, RetroPie is as killer as ever... and when overclocked I can run some 
Nintendo 64, all Dreamcast and everything below. PSX runs well, with only some  games showing slowdown. You can install 'Pixel', a RetroPie add-on that gives  you a standard Raspberry Pi OS Linux-GUI and have a nice on-the-go Linux box  with HDMI out and all ports available for connecting keyboards, mice and other  peripherals.
One thing on my todo list, although not currently supported by Experimental Pi, 
is to load the 'Firmware', drivers, shutdown script and volume overlay on a  standard Raspberry Pi OS (Or Manjaro ARM) install. I'd like to have 2 SD-Cards; 
a great RetroPie build with all the NES/SNES/NeoGeo/Sega/ETC games from my  childhood that I love... AND a standard Raspberry Pi OS build, with all the  PiBoy DMG 'things' working. I'd want to use a USB keyboard/mouse, but it would  be nice to have the 3.5" screen in a pinch and be able to connect MY Linux  system up to any TV/monitor on the go, as needed.
This system cost me about $140, as I bought both the Raspberry Pi 3 & 4 HDMI  connectors. (You must have the one specific to the Pi you're using...) You can  buy one with a Pi 4 installed if you don't like to build, and my link goes to  their FULL system... there are other options available, I believe one doesn't  include a fan so... check em out. 
This thing is AWESOME so far; the only thing I'll say is... (Like other small  run projects) customer service isn't the greatest. First, I had cancelled my  order because it was taking more than a month when I bought.. but they shipped  (and charged) anyway. OK, thats fine... on arrival, they only shipped ONE HDMI  connector (The Pi 4 one.) but refunded me for the other two. After an email  they shipped out a Pi 3 connector free of charge, (Thanks!) but no Pi Zero  connector. (They are 'out of stock'.) Also, my unit has what looks to be....  black smudges UNDER or INSIDE the LCD panel. They almost look like... ink?  Or... black smudges; weird thing is when the LCD turns on they completely go  away... I emailed them and got no response at first, then a response saying 'we 
send out good LCDs', and then asking for photos. Photos were sent and they  failed to respond for 2 weeks. After another round of emails I got, 'Send unit  in and we will inspect and repair'. I think they should have sent a replacement 
LCD, and had me mail the smudgey one back upon arrival of the replacement...
Anyway, I'd buy again because the product is so good.
As promised, here is the description from Experimental Pi's website:
-----
PiBoy DMG is a complete hand held gaming system powered by a Raspberry Pi.  PiBoy is compatible with the Pi 4B, Pi 3B or Pi Zero. With the Raspberry Pi 4  take emulation to the next level. Play N64, PSP, Dreamcast and more games like  never before.
The PiBoy DMG system is not your typical retro game system. It utilizes the DPI 
mode of the Raspberry Pi which allows games to run at frame rates up to 60fps  without affecting the performance of the RPi. It includes an accurate D-pad,  Analog Joystick and 8 button play with dedicated Select / Start buttons. PiBoy  DMG fully manages the Raspberry Pi 4 or Pi 3 with active cooling and safe shut  downs. Built-in calibration and test menus make setup a snap.
PiBoy DMG Kit comes partially assembly. Just add a Raspberry Pi of your  choosing. Easy to assemble and setup for a complete beginner.No soldering  required.
-----
|07p|15AULIE|1142|07o
|08.........
--- Mystic BBS v1.12 A47 2021/01/26 (Raspberry Pi/32)
 * Origin: 2o fOr beeRS bbs>>>20ForBeers.com:1337 (1337:3/129)