My father, who has been a mechanic for over 40 years showed me how to tighten the belt with a big flathead screwdriver. One that is 16-18" long with a thick diameter. Most alternators have a spot were a screw driver or crowbar can be inserted and pushed in the direction of tightening the belt. The locking bolts of whatever you are putting on should be snug but not tight. You want it to pivot but not too easily.
So you push on the screwdriver, using it's leverage to tighten the belt. As you are doing this, you begin to tighten the locking bolt. Essentially, push about as much as you can and then tighten bolts. Now try to strum the belt like a guitar string. When it is loose it makes a low sound. As you tighten the belt more, the tone of the belt will become higher. You want the tone of the belt to sound a little high. I have stuck to this after installing new gates belts and having both alts rebuilt and no problems with squeeling yet.
Finally, the tool looks nice, but it is 17$. You could buy a big screw driver for less than 15$ and you would use that more than you know for a variety of jobs. The belt tool would sit in your garage and take up space.
