I started with only IP products and even had a little bit of the mindset "go big or go home", meaning why bother when you're not using the actual IP products. They were so expensive though, and when I was spending more on a month of IP products just for me than I spend on an entire month of groceries for our family of four I knew I needed to adjust my priorities.
I have to admit, like some PP have pointed out I loved having a coach to lead the way, and will probably go back to her if I'm still in phase 1 when my husband deploys (because my grocery bill will go down even further!). The simplicity makes it so easy, and while I haven't tried the prodi-diet products I've just purchased, I did find I was satisfied longer with the IP packets v. EAS shakes.
If you can swing it I would totally recommend starting off with a coach. Mine was available 24/7 and invaluable to me when I was first starting.