It blocks like maybe 25% of all flash for me. Not adequate at all.
In fact, I don't think it really can work in any real sense as an actual blocker since chrome doesn't provide an API for that. As I understand it, the best it can do is to remove the flash after the page has rendered.
https://chrome.google.com/extensions/detail/cdngiadmnkhgemki...
But what you've said is true, FF's FlashBlock has much better control over Flash because of the control it has via the API. Chrome doesn't offer the same level of control to extensions, so they're all just going rewrite the page on load. That's been good enough for me though.