My house sits on a hilly lot and every time I used the ladder to clean out the gutters or do some painting, I would have to get some scrap lumber or bricks to level my ladder.  This was not only inconvenient, but unsafe as well.  I finally broke down and purchased these levelers and they work great.  They took about 10 minutes to install and are easy to use.  They are also significantly cheaper than the Werner levelers.  I have since installed another pair on my other ladder.  For me these are a must have item and I highly recommend them to anyone who has to use a ladder on uneven ground.