The main reason i tend to avoid Affiliate Programs that have their own Opt-In system is because the owner of the program is blatently taking advantage of your traffic to build his own Mailing List which he will use to generate his own sales, possibly stealing yours.
Opt-In Mailing List
This is a prime example of an Opt-In Mailing List, this Vendor is creating his own list of potential customers for which he will regularly email about updates to his Members Area etc and also promotional emails for other Products on Networks like Clickbank.
Now lets say you send targetted traffic to this web site, you will probably end up with a few sales but for all the sales you dont generate he will have on his “list” so that possibly in the future they signup but when they do you wont be getting credit for it.
I run quite a few Programs on Clickbank and i try and avoid this tactic as the last thing you want to do is piss off the people who are promoting your product as these are the main driving force for sales.
I did a quick PPC Campaign promoting this product that has its own Opt-In system and here are my results…
Now this was 100% Targetted Traffic as i was using PPC, 1812 Total Hops and 0 Sales.
Now this vendor has potentially added 1812 People to his Mailing List and these are all potential Customers, will i get credit for future sales from these people? will i fuck!
It is a slimey way for a vendor to steal sales and i recommend you try and avoid any Affiliate Programs that have a similar setup to this one.
P.S I lost a lot of money doing this test to show you how much of an impact this has on your Promotional Campaigns so you have been warned! 
