IS is one of most complete programs I had the oportunity to try. It can be really challenging, especially the Rings version.
I already did 6 goes, and I am on my 7th (been doing it before Praxis was a thing). Fun thing about it is that no matter how many times you complete it or how strong you think you are, it is always one step ahead of you, and there is ALWAYS something you can work on or improve. Ideally for somebody looking fore bulletproof body without pains and aches.