Please help by testing it early, if you can. You can't really lose: lots of bugs have been fixed in the past month or so!
Does 1.4.3 use the same scripting structure as previous releases? Or does it cripple the older coded blocks like 1.5 dev?
I have many blocks that were crippled when I starting testing 1.5 dev that I have been unable to repair (RSSFeed Plus and random_quotes to name a couple). I have, however, been able to repair the HTML blocks without a problem using the documentation that is included with 1.5 dev.
The trunk (ie 1.5 dev) is development code for developers to work together and make larger changes. In the case of blocks, only some 3rd-party blocks will break in the new block structuring (all the standard blocks were updated at the same time). Unfortunately this was necessary to get a much more flexible block structure - hopefully it won't happen again.