AFAIK, you have to be running Safari 6 to use this update. I banned it from my Lion installation because the iOSified version is crap. Here's why:
The unimproved, clear history option, which does more than that (check the help files); unibar URL/search window, trying to get one thing to do multiple tasks (Apple being like a lemming and following the browser crowd); loss of the appearance pref and inability to change standard and fixed fonts and their sizes, via the GUI (even though there is a way using the Terminal defaults command); and, the utterly useless resizable tab bar spanning the entire browser window. None of these changes are needed or required for a useful Safari, but just an attempt to have the computer version mimic the iOS versions.