It will make a decent table wine, nothing special but okay for an everyday wine. Be careful and watch out for juices that contain sorbate, metabisulfite, or Benzoate as they will hinder a fermentation and if you do make a batch from these do not add any sulfites in the beginning as most of these do contain small amounts of sulfite and the added sulfite may be enough to prevent any fermentation at all. I would recommend 3 - 3 1/2 cans of frozen 100% juice to each gallon.
Walmart has a "Sams 100% concord grape juice" in gallon containers. It only has absorbic acid for a preservative. Comes right out of the container at an SG of 1.045 (many manufacturers set their SG at that level for fruit juices) I started one of these in July of this year and I used 6 gallons of the grape juice, 1 pound of frozen blackberries, and 12 ounce package of frozen raspberries. Mine is still aging under a solid cork. I expect to bottle in Feb. The reason I start out with 6 gallons is to account for my gross lees. I end up with 5 gallons plus a little, which I bottle and cork and put in the fridge to top off later. I think the frozen fruit will really perk up this plain old shelf grape juice. If you don't have the aromas in off the shelf grape juice you can add them yourself. Next time I would back off on the raspberry a bit.
I bottled a batch a couple months ago made with Welch's white grape-raspberry concentrate. More Boone's Farm than Bartlett's, but it was a first try with the grocery store stuff and very cheap. I guess you get what you pay for. I will continue to experiment with it though, because I think the grape juice concentrate as a base has a lot of potential if I also add some fresh fruits and oak chips to enhance the flavor.