The install was mostly OK, aside from the one issue I just mentioned, and a few instances of not being able to find things because of the equals-sign usage... what I mean by that is sometimes, original code is in the format "x=y" and the hack instructions might say to look for "x = y", or the other way around. Those spaces mean what you're searching for and what's actually there won't match, so it makes it a bit more difficult to find what you need.
As for if the hack actually works or not, that remains to be seen. First, I can't really test it at all right now, as this is a very slow time of day for my board, and there aren't a good amount of new posts to mark as read. The board itself still works, and that is always a good sign.

I suspect this hack will work OK; I installed ethank's earlier version, and it worked OK, too, although there was some anomalous behavior noted by some people. But the 2.2.0 upgrade was due out soon then, and I knew that similar functionality was built in, so I didn't bother to troubleshoot it at the time. But we'll see what happens now.
I would suggest to go ahead and install it. Make sure you make a backup copy of your database first, as well as have backup copies of all files you need to modify. If you have installed
any other hacks at all, make sure you actually have current backup copies of your files, and don't rely on the originals, as they will not have any hacks applied to them.