Does he really needed to finish the article with “Sign up to AppSumo.com to see what our new emails look like.”?
It feels so cheap. He should have added the e-mail he was talking about, I use AppSumo and I remembered the e-mail in question, but I bet many people didn't (and they will not register because of that cheap plug!).
I think that a lot of entrepreneurs leave money on the table because they're scared to do something that they think feels cheap. In a case like this, it's probably a tiny minority that would be turned off by this. I'd be absolutely shocked if having a blurb like that at the end of the post would have a negative effect.
It feels cheap not because the blurb but the way how it's written. What I would have done is providing a copy of the e-mails he's discussing and at the end of the article add the plug. "Join AppSumo.com if you want to receive our infamous e-mails stuffed with great deals". (Obviously I'm not a copy-writer)
It feels so cheap. He should have added the e-mail he was talking about, I use AppSumo and I remembered the e-mail in question, but I bet many people didn't (and they will not register because of that cheap plug!).
edit: punctuation and grammar.