The biggest misconception there is about polygamy is that many women don't want it.
"Every single one" of the women users "made the active choice to sign up, choosing this lifestyle and relationship type themselves," commented Azad Chaiwala, founder of both these sites.
"Through polygamy, women get a recognised and acceptable form of relationship that both parties invest time and effort in."
Speaking to HuffPost SA, the British businessman said he reckons his sites are popular with women because polygamy "safeguards" their rights in an "honourable manner".
A mistress is generally unable to choose the direction of the relationship and can't talk about it to anyone. An affair is not recognised by friends, family or the community, and it can be ended with a text message, he said.
Through polygamy, on the other hand, "women get a recognised and acceptable form of relationship that both parties invest time and effort in", the 34-year-old explained.
Chaiwala, who started Secondwife when he was in the process of finding a second wife, dismisses the idea that polygamy makes it easy for men to be promiscuous: "The truth is far from this. Easy is an affair or prostitution, where women are treated and priced as commodities without any human feelings: you use, you pay and walk away."
He argues that polygamy takes into account women's need for safety, security and reliability.
The businessman also dismissed the idea that only financially desperate women enter into polygamous marriages. The women who have signed up to his sites are "lawyers, businesswomen, doctors and teachers," he said.
"It would be nice if men don't take women with no careers, so it does not become about means," famous television polygamist Musa Mseleku from KwaZulu-Natal told HuffPost SA previously. "Doctors, lawyers, engineers, well-to-do women (must be taken), so that love becomes the common factor."
Mseleku also pointed out how polygamy works well if it's a choice for both men and women. "Once it becomes a choice, sharing or competition becomes a non-issue."
And while Mseleku did not meet his four wives online, he said one question that has baffled him for years is why there are so many women without partners -- a question he is yet to find an answer to.
"Every person must be honest and truthful to him or herself. Can you live life with one person? Start there," Mseleku said. "Don't try to live a lie, because you will hurt many people."
Chiawala revealed that some of the women users of his sites are the daughters of polygamous marriages. "They have opted to use our sites because they want the same lifestyles for themselves and their children," he said.
And while he believes this may not be everyone's cup of tea, he's against polygamists being vilified for choosing this lifestyle.
"Polygamy is above board. Families and communities are involved to create a new family. There is recourse in case things go sour."