The PCB works great after installation and connection with a 1.25mm 2-pin JST cable (I wish the connector size had been mentioned on this page). It's very hard to find the battery model with the 1.25 connector without waiting 2 months for AliExpress delivery, so I bought the connector and battery separately and solder spliced them together.
I already owned the Mammoth20 and bought this PCB to upgrade for wireless Bluetooth. It did not come with the foam backing or cover, and I was disappointed on installation to find that the existing back & cover from the wired PCB have a different layout and did not fit. I had to cut the existing foam back to fit, and just jam my switch pins through the cover in areas where the holes did not line up. Everything worked out okay and the PCB works well, but all the same it 100% ought to ship with the foam back and cover considering there is no way to order them separately.
I've been using it for a few days now wirelessly with no issues but will update the review if any issues arise.