We've been using Chef's Plate regularly for well over a year now. Four nights a week of not having to plan dinners or go for groceries is a win in my book. Maybe it's just because groceries are so expensive here, but even at full price I find Chef's Plate to be no more expensive.
I just bought groceries for tonight's dinner (Chef's Plate doesn't come again until Friday): 24 bucks for a piece of salmon, 3 bucks for a package of mint, plus tomatoes, cucumber, broccoli, and that doesn't count couscous and whatever else we already had in the cupboard that we'll be using. Yeah, tonight's dinner will be better than what Chef's Plate sends, but it sure won't be any cheaper.
Having said that, the Chef's Plate stuff is generally pretty good. I'd say the quality of the produce they send us is consistently better than what's available in the local supermarkets.