We are using the ATS. It is a bit of money, but we are unsure of our future plans; since we may be moving to another state, and I don't know what's in store educationally, I wanted the third-party transcript. It has some advantages too, in the transition between school and home. My daughter likes that aspect of it and I think she feels accountable to her advisory teacher as well. It's fun for the child to get the tests and other work back in the mail and read the comments. The feedback so far is excellent and includes wonderfully senstive constructive criticism.
On the whole I like the curriculum so far, though it still requires a lot of planning. I think you have to be careful with any boxed curriculum because you could just do the bare minimum and feel you're completing it. However, that's nice in a way if you're in a particularly busy time, or traveling, and need to get some work done anyway, rather than let it all slide because you can't create and administer it from scratch.
I will say the art lessons leave much to be desired and I simply ignore them. We do the "picture study," which is nice - postcards of famous works you put up for a while and discuss once, rotating them every few weeks. But the practical art lessons - not for us. We are really strong in that area, though, as I am a fiber artist and crafts person and daughter is a prolific artist herself in all media. If art is not a strong point in your family, I would suggest you rely on more than the Calvert plan there. What do others think?