I use my kettle-bells 4 x weekly. 5 lb, 10 lb and 15 lb. I generally don't use heavier than 15 lb kettle-bell.
I create my own combined cardio & strength training routines using kettle-bells & dumbbells.
Below is a list of the routines that I'm currently working on this upcoming week (posted via my journal)..every few weeks I change my routines, switching up the exercises, # of sets, reps, and or adjusting the weight. This just keep things interesting.
Kettle-bell swings, just by themselves, offers both strength & cardio benefits.

My Combined Cardio & Strength Training Routines