I've owned the 7424 for years and love it, but also would like to try out the UDM to see if I'm missing out on anything. The 7424 used to make my hands numb from the vibrations, so I upgraded to the heavier balance weight, which helped a LOT. Also, it does a little quicker job because it has more inertia with the heavier weight, which means it doesn't slow as easily if I push down too hard. I've never had to push so hard that it noticeably slowed down, if I had to remove a mark that bad I just use a different pad/polish combo.