Nice question. The best SFI gateway for me, is the "first" gateway. Based on my experience, I used both the "first" and "free" gateways, the "first" converts more. I already tried it several times, landing pages with videos converts well. But if you like, you can do a split test for SFI gateways, for example you are doing an e-mail ad, put the same subject, same content for each gateway, you'll have 2 e-mails. Send this 2 e-mails to groups then see the results.
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