Moyes has made a string of shrewd signings during his 10 years in charge on Merseyside.
Moyes said: "I did worry when it was first mentioned about bringing Steven back.
"At Everton we have always tried to do good deals and have always tried to buy at the right age and the right price.
"We had to buy Steven back for more than we sold him for. That didn't sit well with me because I didn't particularly see it as a good business deal.
"But I knew on the football side of things he would make us better. It's been a great deal for us and we're delighted to have him."