i've been using hellofresh for about 9 months. 5 meals, every other week, very impressed with it. The quality of ingredients is high, I tend to buy my meat/fish on the weeks off from a guy I know who supplies restaurants like the Ledbury, and I think the quality stands up to that. The portion sizes are very generous, we often end up with about 1 portion extra for a lot of the meals. You also get a very varied menu, so you are always trying new things. Things are also generally very healthy as well, plenty of vegetables, including ones you might normally not try.
In terms of price, I think its actually good value (although I'll admit i'm fortunate to not be counting the pennies really) although like all things if you're organised enough you can do it cheaper (quelle surprise), so you pay a premium for the convenience. Having said all that, since I switched to it, I reckon my food bills has overall gone down as I waste less and make less random food shops at waitrose.