Mido held talks with the Black Cats boss as the uncertainty over his future dragged on, before finally electing to join Gareth Southgate's men for a £6million fee.
He said: "It was a tough decision, especially after I met Roy Keane. I was very impressed by the way he played but if you go to meet him you see a totally different person.
"But I decided to come here. It doesn't mean I do not think Sunderland or Roy Keane will do well. I really think they will, but it was my decision to come here and now I can focus on doing well."
The 24-year-old striker also refuted reports that his desire to move away from Tottenham stemmed from a disagreement with Spurs boss Martin Jol.
"I have no problems with Martin Jol," he added.
"I believe Martin Jol is a good manager but I wanted to be scoring goals and playing a big role in the team I was in.
"I didn't find myself doing that at Spurs, and that is why I decided to leave."
Mido will go straight into the Boro squad for Saturday's trip to Fulham in a move which effectively spells the end of Ayegbeni Yakubu's Boro career - although Southgate insisted the Nigerian could still figure.
Despite his new side's poor start to the new campaign, Mido insists they are capable of recovering to claim a place in Europe.
He said: "Sometimes players say things they do not really believe, but I really believe this club can finish in the top six.
"After I had spoken to the gaffer, and what he told me about his plans and how ambitious he is with the team, it is easy to see how this club is ambitious and how it has got that sort of quality."
Meanwhile Southgate claimed he was delighted to land the kind of outspoken character which he believes his current dressing room badly lacks.
Southgate said: "If you haven't got players who will stand up and fight you have got a problem.
"It is no issue for me at all. In fact it is one of the reasons why I saw Mido and thought he would be perfect for this club."