We were introduced to Dream Dinners about a year ago. Consistently I've found that I save about $200 a month on our grocery bill. (We buy the 3 serving instead of the 6 serving meals that they offer, because our kids are young and don't eat a whole serving by themselves yet. I imagine you might save more with the 6-serving meals.) I think the reason you save money is that instead of buying lots of ingredients and then only using a small portion, and then having the rest of the ingredient go bad, you're sort of able to "co-op" with lots of other people to share the ingredients. Plus Dream Dinners buys in such huge quantities, they get better pricing anyhow.
It's been a huge win for me, because we get a LOT more variety than we were used to (let's just say I'm not the world's most enthusiastic cook), and by and large the ingredients are quite healthy - not a lot of butter, oil, salt, etc. That, along with not really having to grocery shop, and not having to prep dinner EVER... It's one of those things I wish I'd known about years ago. I hope this helps!