Beware of SEO companies using their own shadow domains to boost the performance of client websites. Shadow websites lead/redirect the visitors to client websites.
Things are certain to look good until the clients relationship with the SEO company prevails. Once the relationship is ruptured the SEO company would remove the redirect set to the client website from their shadow domain and point it to their new client website. This new client could be the competitor for the former client.
Well, the poor client who has actually paid for the SEO company will loose the value of the shadow website link gained so far and ultimately their website performance will dip.
Website owners using the services of SEO companies should be aware of this situation!