Bluetooth 4.1 => AUX from UGREEN speakerphone

UGREEN Hands-free AUX>

By mistake, there is no BT in my machine, and there is a way outreplace the GU with another one, or buy such an adapter. As a temporary solution I decided to save, but the avaricious pays twice, and the goof three times. AHTUNG! The review is short!
A distinctive feature of this device is that it works without a battery, and there is a speakerphone.
Packaging, as always with Ugreen, is up to par

We open it (On the device there are buttons for receiving a call, and switching tracks.):

At the bottom there are two mounting options: 3M tape, or on the air duct grille

The connectors, as always, are of high quality:

We connect in AUX, USB, and I hid the wires in a niche:

Sound quality:
The main question that worried me wassound quality. So here. The subject cuts off the high and low frequencies quite noticeably. And it’s not that there are no lower classes, they are, it’s just a sound like it turned up the volume by 146% and the speakers can’t cope, a characteristic “overload” begins. But this is only on tracks where there is quality punch. There are no problems with mid bass. Here is such a sad story. No, the sound is not disgusting, but worse than through aux.
I note, compared the bluetooth vs aux. And the quality of the aux depends directly on the source. In this case, it was an iPhone. On cheap Chinese smarts, perhaps there will be no deterioration, but it will become even better =) I don’t know ...
Maybe craftsmen, they can solder something inside, change chips and it will become better.
Now I doubt whether it is worth changing the GU to a supporting bluetooth, suddenly there will be the same thing.
The speakerphone just works.
UPD: I understood what the problem of the subject is: the amplifier is not enough. I set the volume on the radio to the maximum, on the iPhone to the minimum (possible) - the bottoms have become better.