From their ‘About Us’ link:
We are a Muslim polygamy matrimonial service brought to you by Polygamy.com. We set up this service as we believed this is a Sunnah we needed to revive. We care strongly about Islam and the teachings of Allah and have built our site with great care and detail. Inshallah we are taking every precaution to be sure that we are in-line with the teachings of Islam.
To show (apparently) that they have ‘responsibility’ on the matter, they reproduce this Quranic quote:
“then marry women of your choice, two or three, or four but if you fear that you shall not be able to deal justly, then only one” – Quran 4:3