Is this a rectangle 120" by 68"? Is it designed to be just a hammock shelter or would it work as a tarp shelter on the ground as will?

You can use this as a stand alone tarp shelter by hanging it between 2 tress and staking it out, or even by using 2 hiking/ski poles at the ends and staking it that way.

I just got one brand new and cheaper off of Amazon.com with free shipping. the material itself is lighjtweight and durable.... but you want to use it as a tarp/rain fly... not a groundcloth. it's pretty durable but too likely to rip if it's on the ground. it's very good size... but it is meant to be used with a hammock or as an instant shelter. the reflective side..... is almost white. not silvery at all

Yes. It appears to be a rectangle and it seems to be very flexible in its use. It is recommended for use with their hammock, but it would probably be great for other things. (they want you to buy the hammock to go with it)