Don't use the J as a hook and don't lever upwards to free a frame as both the downward and upward force can damage hive or frame. If you hold the tool horizontally, the J can be slipped into the gap between the top bars. The turning action will then only apply pressure between the opposing faces of the top bars, causing no damage at all. Using the tool in this way will easily prise apart even the worst propolised frames (and easier still if you use DN 5's).
The chisel edge of mine is wider than I'd like but there again, I've never found any tool brilliant at scraping the top bars because the bees always want to get in the way.