I currently do WW and follow the points plan, but 95% of the foods I eat are the Simply Filling/Core. I do plan to switch to the Simply Filling eventually, but I like the accountability of points.
Also, you can change your payment plan at anytime. If you are paying week to week, you can buy a pass for 4, 12, 16 weeks. But if you choose to buy a pass, they will not refund it if you decide you'd rather pay week to week. Hope that helps!