I never heard of Kettlercise before so looked at some videos.
Kettlercise doesn't look very demanding.  Less heavy breathing than my 12 minute/mile pace jogs.
There are very impressive claims about how much calories Kettlercise can burn, like 657 calories in 45 minutes (24yo F, 5'6", of unknown weight)  
I tried using the calories burnt as function of HR formula* on this page:

https://fitness.stackexchange.com/questions/12435/is-it-possible-to-measure-calorie-burn-from-heart-rate-alone?rq=1

That formula comes up with numbers I think are credible for my calorie burn when I am jogging (*I have a pretty good estimate of my real VO2MAX).

But the HR that would be required for a 24yo female to get to 657 cal/53 minutes, requires all kinds of extreme values in the formula above. VO2max = 50, 70 kg, avg HR = 195.  Do those numbers make sense(??)  Is the formula that inaccurate?

Or would I be right to think that Kettlercise energy expenditure is probably being over-hyped?