Stable and precisely what you want more?

The installation worked fine, and I must say that I found it easier at first to screw the speaker into the adapter and then the adapter into the door as the other way around.
The adapters make a strong impression, but who has value on high quality sound, which should rely more on the MDF adapters.
I could not tell the acoustic disadvantage, but this certainly is also due to the lack of insulation of the door and the entry-level speakers.
Nevertheless, I can recommend this Adapter to anyone who conveniently installed loudspeakers in the accessories in its Corsa B or Astra F or the like.