Stillwell Audio's Event Horizon is a VST based limiter plug-in. I didn't have any problem installing the plug-in, as the process was easy and pain free. I got the plug-in straight from their website, and the whole process of downloading and installing it only took a matter of minutes. The interface of the software is about as user friendly as you can get. It simply has knobs for threshold, ceiling, and soft clip, and that's all that you have to work with. The plug-in also has VU meter for both input and output. A manual isn't necessary as most users should be able to figure out how to use one without any assistance.
I'm currently running the Stillwell Audio Event Horizon on a Mac Book Pro that has a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM. I run the plug-in in a Pro Tools LE 7.4 system with a Digi 002R audio interface, but you need the Fxpansion VST to RTAS wrapper or something like it to do so, as this is a VST plug-in which is not supported in Pro Tools without the converter. This is the type of plug-in that takes up a very small amount of processing power, but all systems are different so how well it will run solely depends on this. Having said that, if you are currently running plug-ins on your system without a problem, you shouldn't have a problem here.
I've recently been exploring the plug-ins that Stillwell Audio has to offer, as they are very cheaply priced and are generally of a pretty high quality. This is where having the Fxpansion VST to RTAS converter really comes in handy for Pro Tools, as it gives you access to a whole slew of inexpensive VST plug-ins, most of which aren't great but you can find some good ones like the Event Horizon. This is a very heavy limiter, and isn't something that I use unless I'm looking for this particular sound. If you're looking for some plug-ins to build your suite with, I'd definitely both Event Horizon and Stillwell Audio as an inexpensive line of nice sounding plug-ins.