I feel that (and this is just my opinion) that the grape skin packs in the wine kits are dual purpose:
They give the benefits of fermenting on skins for added mouth feel body and color, and tannin from the seeds, but if you've ever taken a SG before you've added the grape skin packs provided in kits, you would have gotten a lower SG than you would after you add the grape skin packs and stir them in real well, they contain a thick syrup that raises the Gravity level.
The Grape skin packs that I bought from M&M, the all grape packs, do contain crushed grapes, juice, and an occasional stem or two, the same product that you would get from crushing and destemming grapes yourself.
I'm not saying that one is better than the other, they each serve their purpose. I plan on making my own, as soon as my grape order comes in.
Elmer, the grapes do not have to be the same kind that you are making, a safe bet would be to use Merlot grapes, you can use them on any kit and juice bucket, with the exception of white, I've only recently tasted a Chardonnay fermented on its skins, it was interesting.
If you have a ton of grapes, find one that is mild, and use it!
Gwand - the "allgrape" grape skin packs appeared that they were stored at room temp, the first grape skin packs that I found in CT had to be refrigerated. I'd ask the seller.