I did some initial testing with the amplifier board, wiring in some speakers on the bench to run the amplifier through it's paces.

The board is a simple 2 layer design with most traces on the top side..  There were some lose solder balls on the board, so the quality is not the best.  The first board I got had the ferrite broken on one of the inductors, but the replacement was fine.

Speaker outputs have screw terminals and are labeled.

DC power input is labeled 12-24V with a barrel jack.  While not labeled, it is center positive.

There are 3 tact switches for bluetooth control.

Amplifier section

In theory the board is based on a pair of TI TPA3116 class-D amplifier chips, each doubled up to provide a 100w channel.  I did not pull off the glued on heat sink to look, so I can't guarantee they are genuine parts, but it seems to work pretty good.  The output is very powerful given how little power this module takes, barely getting warm.  There is some hiss when there is no signal source, pretty typical for low cost consumer audio.

Bluetooth section

The Bluetooth interface is handled through a BTM835 bluetooth module which is soldered on the board.  I couldn't find much information about the module, except for this document which I think was part of a legal filing.  It at least includes a pinout, and seems accurate.

The range is not the best, as indicated in some of the product reviews.  I could always maintain a solid connection with my phone within about 16 feet.  Past this, connection depended on who or what was in between, and other factors I couldn't be sure of.  Sometimes I could maintain a connection through walls and people about 30ft, other times it broke up around 16.  I may try to connect in the wifi antenna in place of the PCB trace antenna on the module, but that may be more than I want to put in the project.

The play pause button worked as expected.  The skip back/volume down button and skip forward/volume up button were different.  pressing and releasing causes a track to be skipped.  Holding the button for a second changes the volume. 

Noise

When powered on or off, there can be notable speaker pops, which is not good.  I will need to see what can be done about this.

With the bluetooth interface, it will play a connection tone when it is initially made.  This is fairly loud, much more than one would want.  This complaint can also be see in product comments.  When adjusting the volume from my phone, there were also beeps each step.  While I can see the desire here, to offer feedback, they can be annoying, and won't work for my application of setting up audio for a room.  These will also have to be worked around.