I am doing Rushfit, started it about a week after finishing insanity. I am enjoying it and feel stronger, and my abs are getting a nice shape and strength to them. I also run and do one or two insanity workouts as the cardio part (rushfit leaves you to come up with your own cardio). I would recommend a reasonable fitness level before starting although there are plenty of modifications for the beginner.
I got bored with Rushfit, am starting Tapout in the am, mixed up with a bit of insanity!!! Can see definition in my arms n legs, have a bit of fat around my abs tho so not quite visible haha