I've only tried fruit juice once and it sucked, but i was new to brewing and tried to make a pineapple apple cider. Since then, i have found that whole fruit and concentrates seem to work better in the secondary. If you do try fruit juice, make sure to have it free of any preservatives like sodium benzoate, potassium sorbate, or potassium metabisulfite. Ascorbic acid is fine as a preservative though. Please post if you go through with a fruit juice. I'd like to know how it turned out.