I've done Simply Filling although I mostly like Points Plus.
Pros of Simply Filling:
1. Easy. Not a lot of weighing or measuring or counting points (There is some for things that aren't Power Foods).
2. It is a healthy eating style by and large. I mostly follow South Beach for types of foods to eat and Simply Filling is really a lot of overlap with that. With Points Plus it is perfectly possible to eat a diet that is really not all that healthy. With Simply Filling the odds are greater that you eat a healthy diet.
3. I did lose weight with it.
Things I didn't like:
1. Some healthy foods aren't Power Foods and you really pay a price for eating them. For example, nuts aren't a power food. Yes, I know they are high calorie so I can understand why they should be limited. On South Beach for example they recommend 1 serving a day. I wish Simply Filling just said you could have 1 serving of nuts a day. Yes, I know I can count points for them but if I do that then I basically don't have points available for much else.
2. Lowfat cheese isn't a power food and you have to count points for it. WW still seemed stuck in the old anti-fat mentality. They allow nonfat cheese but not lowfat cheese (well, you can count points for it). I would rather see lowfat cheese be a power food.
3. In general whole grains are power foods. But there are some caveats that had an issue with. Whole grain bread is not a power food unless it is reduced calorie bread. I can accept that, but the thing that really bugged me was refined grain white bread doesn't count points and can be eaten on Simply Filling if it is reduced calorie. This seems to fly in the face of the whole philosophy of Simply Filling. Simply Filling really recommends whole grains. You have to eat brown rice and whole grain pasta, for example, or you have to count points.
But when it comes to bread things are backwards. You have to count points for whole wheat bread (if it isn't reduced calorie), but you don't have to count points for reduced calorie white bread. I don't agree with that. I think white bread - reduced calorie or not - should count point. And if you have a choice of regular whole wheat bread or reduced calorie white bread I think that WW should encourage eating the whole wheat not the white. But, it doesn't work that way.
4. The reason I lost weight on Simply Filling kind of fast was that I ate a lot less calories than I eat on POints Plus. At the end of the week on Simply Filling, I had use 53 weekly points - all of my 49 weeklies and 4 activity points (which I never eat). Note that I did this even though I ate zero bread that week, and zero pasta (I was working on avoiding gluten). It is just that I eat enough things that are not bad foods but aren't power foods that I was constantly having to spend points. I would never have made it had I been eating gluten.
For that week, I calculated how I would have done with POints Plus. For that same week, I would have eaten my daily points plus only 8 of my weekly points. I would have had left 41 weekly points and all my activity points.