Stereo to surround is a huge issue that a lot of people face when they start remixing old movies for today's sound systems. There are two different versions of this -- the UM225 and the UM226. They're both almost identical, except that the UM226 has the extra .1 channel for the sub. Why they decided to break these plugins up like they did, I'm not entirely sure. The plugin has adjustments for the various five bands plus the sub, different modes and filters you can adjust, and tons more features that would take quite awhile to describe. To enable this, simply put it on your master buss and start mixing. It's really that simple. I've never really read the manual, so I can't comment on how well written the manual is, but Waves generally has some fairly nice manuals.
Waves is pretty famous when it comes to both compatibility and stability. For one, these plugins are rock solid. I've never experienced any problems using these. There have never been any freezes, glitches or anything bizarre going on, even with a fairly heavy usage of other VSTs in the DAW. This is also cross platform compatible, so anybody on an Apple or Windows computer can easily use this without any problems. There is one problem, however. In OS X, this plugin is 32 bit only. That means that your DAW needs to enable a special bridge application if you want to use your environment in 64 bit while utilizing these 32 bit plugins. It's does it automatically, but I'd like to see the next revision be a 64 bit plugin if possible. I've been using the Mercury bundle for half a year now, and it's been a wonderful experience.
I've used this with varying success on different mixes for my own home movies and whatnot. My personal system is a 5.1 system, so I always reach for this over the UM225. I don't really see the point of using the UM225 when the 226 can do everything the 225 does and then some. It's a very solid plugin, and it work as advertised, but don't expect it to start working miracles here. It's still somewhat limited as to what it can do overall. Solid plugin, though.