The Ecuadorian arrived in south Wales from Mexican club Morelia last month, joining the likes of Bafetimbi Gomis, Gylfi Sigurdsson and Lukasz Fabianski in making the move to the Liberty Stadium.
And Rangel says he has seen enough in training to believe that Montero will cause problems for Swansea's Premier League rivals this term.
"He offers a lot of speed down the side, he can play with both feet and he can run at defenders," Rangel told the club's official website. "You can see in training and in games that you have to try and double up when dealing with Jefferson because one-against-one he is quicker than anyone else.
"You need an extra defender to cover for you. In training, because I play on the right and he plays on the left, I can see what he's capable of.
"Hopefully he can carry on and show that confidence in one-versus-one situations in the Premier League."
Swansea were on the receiving end of a 3-0 home defeat at the hands of Villarreal in their final pre-season friendly on Saturday, but Rangel says the Welsh club will go into their opening league fixture at Manchester United next Saturday with confidence.
"Manchester United are a top team," he added. "With a new manager, they will be very motivated, so it's going to be a tough game.
"But we will go into the game feeling confident. When you go to Old Trafford, you know it’s never going to be easy, but we will be giving it our best."
