Yes, they are awesome for weight loss. In Kettlebell training you are performing compound exercises in a range of motions. This means you are working multiple muscle groups at once, therefore, increasing the intensity of the exercise and burning loads of calories!
The American Council on Exercise conducted a study that concluded the average person can burn 400 calories in just 20 minutes whilst doing a kettlebell workout!
That works out at 20 calories a minute! 4/5 times that of normal weightlifting and nearly twice that of running.