I've finally found someone who can deliver those yardbags of soil
directly to my backyard but now i'm trying to figure out what I want
delivered.

My plot is clay. If left open to the air it turns greyish and gets
very very hard. Impossible to work with when dry. Last year i used a
layer of generic "black earth" on top which worked really well. I've
posted and read a bunch to find out I should dig in organic matter to
help make the clay more manageable in the years to come. Things grew
well in it last year but, like i said, it's impossible to work with if
it gets direct exposure to the air. I plan on getting this delivery
company's Multimix (manure, compost, peat, sand) to dig into my clay.

My question:

I want to get two bags. Will such a multimix work well as a top 2
inch layer to do the actual planting in and keep the clay from drying
out? Or should I make the 2nd bag as their generic black garden soil
like last year, which seemed to work well, for that very top layer?

Iis there any advantage to 'black earth' over a mix of manure,compost,
peat and sand?

Any thoughs appreciated.