Apple cider vinegar is supposed to have many benefits including dissolving stones. Do a search on google and you will find many sites that discuss the positive benefits. It appears as though one gets more benefits from the vinegar than the apples alone but that may be due to the acetic acid rather than the malic acid. Perhaps someone else can shed some light on this............??
I tried to do research on whether the vinegar had a higher content of malic acid than apples or apple juice but could not find any info. I would assume that since a large amount of apples go into making a small amount of vinegar that the malic acid content would be higher than the apples alone but those are just my thoughts.
I would also assume that taking it between meals would not have any advantages to having it just before / with meals as you are getting the malic acid regardless but once again, these are my thoughts only.
Maybe the ideal thing to do, and with the lack of concrete info, taking it in apple juice would cover all the bases provided your body is OK with the apple juice.
I drink 2 -3 glasses a day but I also take liver herbs so I don't really know if it is the vinegar or the herbs or both that I am benefiting from.
Hope this helps.