I think they are a fine temporary vessel. As others have said, I'd be concerned about getting them really clean and oxygen permeation for longer term storage. See what they are made of.
The designed for wine plastic containers I use (Spiedel, Flextank) are made from HDPE (high density polyethylene). I've stored wine in there for a year, no problem The Brute cans I use for transfers and occasional ferments are LDPE (low density). I also have some Better Bottle plastic carboys made from PET (polyethylene terephthalate). I've only stored white wines/skeeter pee in the PET containers, which are only aged for 4 or 5 months and they have been fine.
I would trust the plastic water cooler jugs for a batch of skeeter pee, dragons blood, or a quick fruit wine, but I wouldn't try to make a nice red wine from grapes in them.