RK-7157G — 2-DIN Head Unit

RK-7157B is same except that it lacks the built-in GPS Navigation feature
RK-7156G and RK-7156B are very similar

(The "G" suffix means that the unit includes a GPS Navigation unit [though maps usually are not included].)

User Manual:
https://burtonsys.com/RK-7157G/RK-7157G_user_manual.pdf

Sold on...
• AliExpress
• Amazon
• eBay
• In quantity: ReakoSound's own site
• Successor product is RK7160G (supports radio in background during navigation and when backing up)

Demo:
https://youtube.com/watch?v=1i0yErHFOy8

Remarkable functionality for the money, but it has a few flaws:
• Poor quality documentation (see user manual, above)
• Poor menu / user interface usability
• Touchscreen is often unresponsive — and it is fragile, so don't tap too hard or you'll break it!
• The built-in microphone for hands-free bluetooth use is unusable — other party can't hear you unless you yell
• Advertised rear connector for external microphone is missing (but I added it — see below)
• Radio or music is silenced while backing up and during navigation announcements (apparently fixed in RK-7160G)

Click the photos to enlarge them...

Incorrect info in product description
(RK-7157 lacks the advertised rear external microphone jack)

But I managed to add the missing microphone jack (by removing the useless internal mic)

(YouTube has a video showing someone adding a mic jack to an RK-7160G.)

Inside view, showing the two PCBs (after I replaced the broken touchscreen digitizer glass)

Top left corner of front PCB, rear view (behind mic)

Top left corner of front PCB, front view (two views, showing mic and IR receiver at top)

I salvaged a microphone jack and wire from an old PC, and installed it in the RK-7157G:

Step 1: soldered the ground side wire to the PCB

(Oh my, magnified like this I can see how ugly my solder joint is! How embarrassing!)

Step 2: Broke off old mic, and clamped signal wire to PCB with hemostat, before soldering it.

Step 3: soldered the signal wire, routed the cable (held in place with hot-melt glue), and mounted mic jack on back in existing hole (friction fit, reinforced with hot-melt glue)