I think it depends what your overall aim is? Is your main objective to lose weight, become fitter, get a more athletic/toned physique, improve your overall health?
Insantiy looks like high intensity interval training which is really effective and still utilises bodyweight moves like push ups and squats etc which are really effective and I'm sure any routine like that will help with weightloss providing you are eating in a healthyish fashion.
However, I think the great thing about weights are that they improve your bone density and help to prevent osteoporosis, they help to raise your metabolism, and more women should lift weights as after their mid thirties they begin to lose muscle mass etc, so there are great health benefits to be had as well as helping to create an athletic shape.
I struggle to see how you can do P90 without needing a huge range of weights to be really effective. In the routines I do at the moment I use anything between 3 and 35kg dumbbells and up to 70kg on the barbell, depending on what exercise I am doing.
It's a shame you can't hire them for a week so you can have a look and see which you prefer. There seem to be loads of series like this in the states, the other one I keep hearing about is chaLEAN extreme here and Cathe Friedriche here sts strength series looks great, a bit like body pump, but it costs a fortune. How come in the uk we are stuck with celebrity endorsed rubbish??