You should be careful how you use the term "flashblock". For desktop web browsers, most "flashblock" tools only hide the flash objects. They do this to not break compatibility as thoroughly, but it unfortunately means that browsers running flashblock are still generally 100% compatible with flash-based security exploits. It seems reasonable to expect that such tools can hardly improve the battery life over unrestricted Flash.

I don't know if this applies to Android, but on a MacBook Air, you're best off using Adblock and/or NoScript to ensure that flash objects and advertising scripts never even get fetched over the network.