After installing Surfshark it seemed to work perfectly until, using various DNS leak test tools I checked it out. Although Surfshark showed the connection to be secured ALL DNS leak tests revealed my true isp. I was not protected at all. A BIG wake up call. I am willing to concede that perhaps there is some peculiarity to my system but I urge, in the light of my experience, regularly PERFORM A DNS LEAK TEST before going further.
I have uninstalled the extension and rely on my paid desktop Surfshark subscription.