These kinda questions are so rare these days--the kind I can answer intelligently.
There are no cons except that you have to have one on you to string your bow. Other than that it is altogether better because it is safer for you and the bow.
Your stringer has a cup and a loop on the two ends of a string. Your unstrung bow should have the bow string loop slid down over your upper limb and the other end of the bow string in place on the lower bow tip.
Place the cup of the stringer over that lower bow tip, flip the bow so it is facing toward the sky, let the stringer slack fall on the ground while you place the stringer loop over the upper limb and down past the bow string loop which is slid down the upper limb.
On the stringer loop there should be a pad, block, or something to set on the face of the bow limb. Place that thing on the limb below the bow string loop. Step on the stringer slack and hold it down on the ground at a point about in the middle of the stringer.
Slowly raise the bow skyward whilst holding the block on the limb and with your foot on the stringer until the slack is taken up and the bow starts to bend. With just a little tension of the limbs the bow string will begin to slacken allowing you to begin sliding the bow string loop toward its bow tip.
At this point I like to slide the block thing toward the bow tip also, for better leverage. So, the cup of the stringer is in place on its own, you have one hand pulling up on the bow at its middle, toward the sky, you have one foot on the stringer center and your other hand is sliding the bow string toward its tip. The more you pull up on the bow the more slack you get on the bow string so that you can slide the string loop onto and in place on it's bow tip.
When you've worked the string loop fully onto the bow tip groove you can slowly lower the the bow and allow the tension to transfer from the stringer to the bow string until the stringer goes slack. At that point you can remove the stringer.
Reverse steps to destring................sb