There are no compatibility issues with this plug-in as far as I am aware. We have it installed on our Pro Tools HD system at the studio and I know there weren't any problems getting it installed. The manual explains it clearly though there aren't a whole lot of functions anyway. The setup of this plugin didn't take long and was relatively painless. The typical functions are right there on the plug-in when you open it so I'd say they are definitely easily accessible.
This isn't exactly a very demanding plug-in when it comes to processing power, so I'd say overall I've never had a problem with it's performance. It really is one of the least demanding plug-ins in terms of RAM. It's really stable as well.
The basic function of this plug-in is to provide a level for the audio you are using. The difference between this plug in and the others is that it gives you a more accurate reading. This means that it gives you a reading based on which frequencies are louder in the human ear. This way it'll give you a visual representation of howl loud everything is in terms of human hearing, rather than how loud it is mathematically, which is what the meters in Pro Tools will give you. There's technically two meters, one gives you the average volume of the track in question, and one gives you the peaks of that track. There are various settings which will allow you to tweak the meter further to get different readings but that is the basic function.
While there aren't any problems with performance, I see no real need for this plug-in except for one instance. That instance would be if you are working with less-than-stellar monitors. If that's the case, and you know that what comes out of those monitors during a mix isn't really going to work well, you might want to use this meter to get a better ballpark reading. But otherwise, I'd say use your ears first, and let them tell you what's too loud and what's not. That makes this plug-in pretty useless overall. I don't want to give it a really low score because it works well for what it does and it's cheap, but I doubt most people will really need it at all. It's not something you'd use to process the sound at all, so basically it's not the most useful plug-in.