Benitez landed Rondon on a season-long deal in the summer from West Brom, with Dwight Gayle heading to The Hawthorns.
Benitez said: “It is always a risk to sign anyone because the Premier League is very demanding.
“But when they have been here in the Premier League before and after they come here and they perform, it is an easy decision.
“Everybody can see he is doing well.
“He is playing well, he is scoring goals, he is giving others the opportunity to go forward, he is doing a lot of good things.
“In terms of his attitude on the pitch, he is working really hard.
“And for a striker who is on his own, that is not easy."