The real problem with them, besides the hollow handle that can't be cleaned, is they are somewhat permeable to oxygen. Meaning bad things for your wine. The better bottle style plastic bottles do not have this problem, not the hollow handle. They are perfectly safe to use.
I live in Costa Rica and glass carboys are just not available. I have been using the plastic water carboys for over 10 years I use the water from these to make the wine and return for deposit those I used for last years wine. Never had a problem.
The plastic office water cooler jug serves one great purpose for me. Rack out of a glass carboy into it. Clean the glass carboy. Transfer right back into the freshly cleaned and sanitized glass carboy. Immediately clean out and sanitize the water cooler jug.
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.