I've been using both since 2005 (DBs) and 2007 (KBs).
They are similar in some ways, but very different in others. Certain movements can be done with both, but the shape & versatility in the grip of a kettlebell makes it more suitable for some (and sometimes DBs are better for others).
For example - a heavy swing cannot be done properly with a dumbbell. This is a compound movement that uses the whole body. The clean & press is much easier with a kettlebell. You can also do deadlifts with a KB as opposed to requiring two for deadlifts. There are a million others. You can also do HIIT/"cardio" with KBs, not as much with DB's.
Both are great and IMO both should be used depending on what/when.
Maintainer 2004-2009/3 Pregnancies/Maintainer 2013 - Present
Last edited by sacha; 05-10-2013 at 01:15 PM.