By cloned I mean sites that share their user base, even if their user interfaces may appear superficially different.
From the experience of our own contributors, we have long known that the following two sites share the same SB profiles:
SecretBenefits (SB)
SugarDaddy (SD)

From internet searches, one can see that LuxuryDate (LD) is another clone, though no one here ever seems to have used - a third site.

More recently we here have discovered that OurSecret (OS) also shares its user database with SB and SD. A fourth site!

So in total we have the following four sites as using identical user databases:
SecretBenefits (SB)
SugarDaddy (SD)
LuxuryDate (LD), and
OurSecret (OS).

The question then becomes, why? I can think of two answers:  
- First, multiple sites can make different pitches. One for luxury, one for secrecy, one for a straight appeal for sugar daddy, etc. So one site may hook a user that might not have bitten on one of the other pitches.  
- Second, most people probably don't know that these sites are clones. So SDs may sign up for more than one site, increasing revenue.  

Final thought - is the pricing the same for all four sites, or is one cheaper?

I don't know about the other clones, but I paid $89 for 200 credits on Secret Benefits.  I've come to not trust them.  I rarely get responses, and the ones I get are invitations to see an SB's "secret" photos and see the "answers" to her "secret" questions.  I think, at bottom, SB is a scam.  But I'll give the orchestrators credit.  It's a good scam... and a lot of work was invested in putting it together.  On a certain perverse level, one has to admire a talented scammer.  ))

Flat monthly rates from SDM and SA are for me.  Ashley Madison was a scam and who knows how many profiles are fakes or just copies from other SD sites when you have to pay per contact.

And I'm getting plenty from either of these two.  So why take the risk?  Spend hundreds of dollars on the off chance you find some exotic hotty on a different site?  

Our Secrets operates the same way. You must spend credits to send and receive messages, as well as unlock private photos/videos/questions. After you have done all that, the POTs become radio silent—pure scam.

I agree with this. My preliminary tests with SDM are showing very good response rates. SA and SDM, are keeping me very busy with decent prospects, some of which are turning into successful BCD's and what appears to be some decent keepers.  

 
There are lots of scammers and flakes, as always, but if one is willing to mine the rocks there is gold in them thar hills. The other sites mentioned seem like rip offs.