Product review (4 stars): I hope the belt stretches
I bought this kit when the old belt was slipping on my ten year old Whirlpool dryer.  I didn't know for sure what I might need to replace so the kit seemed the logical choice.  In my dryer, the idler/tensioner was not a pulley.  Instead of a pulley, it was a half-circle piece of metal with some thick plastic covering it.  The belt had worn a fairly deep groove in the plastic so I was feeling pretty good about replacing that with this shiny new idler pulley assembly.  I compared the old belt to the new and the new one was perhaps an inch shorter so obviously the old one had stretched.
The two wheels included in the kit seem to be not as good quality as the ten-year-old ones but I replaced them anyway.  To get the old wheels off you need to pry some small triangular retaining clips off the shafts.  That wasn't too difficult but when I went to replace those old retaining clips, the new ones were quite brittle and a couple of them broke.  Fortunately I had not destroyed the old ones so I was able to put those back on.
After reassembling the dryer and starting it, I was quite disappointed to hear how noisy it was.  The problem was a combination of the new belt being shorter and the idler now being a pulley that was riding against the drum.  The drum on my dryer has an indentation on one side that sort of forms a fin on the inside of the drum.  With every revolution of the drum, there was a fairly loud thump.  This was the idler pulley hitting that indentation.
The noise has gotten less after a few weeks of use and I hope it will go away completely as the new belt stretches a little more.
I'm happy I bought the kit and installed it but I'm pretty disappointed in the little plastic triangular retaining clips.