AIR plugins are part of the set of plugins that come together with Pro Tools. AIR stands for Advanced Instrument Research, and these are highly versatile plugins that really help expand the overall usage of Pro Tools. First of all, there are no compatibility issues with these plugins as they're made exclusively for Pro Tools. That means no unexpected crashing or weird bugs. I never read the manual on this, so I can't really comment on that. These plugins are easy enough to use that you shouldn't really need it.
I find that AIR Distortion works best for those wanting to add some slight grit to vocals or those working with electronica music. For guitars, this isn't something you want to use; guitars are usually already distorted. It's a powerful distortion that can get out of hand if you're not careful, so be sure to use it lightly.
I never experienced any performance issues with these plugins, and the reason is that they're made exclusively for Pro Tools. Because of that, everything is rock solid. I use a Mac Pro Dual Quad Core machine, and while Logic is my main DAW, Pro Tools is what I've been experimenting with lately, and I can see why it's considered the best DAW out there. I never had any issues when it came to RAM or slowdowns, but it could also be because my machine is fairly hefty. I've only been using Pro Tools for a few months, so my opinions may change in the future.
I don't use this one quite as much because it's not really meant for guitars. I've used it on vocals with success, but since I'm not a huge electronica guy, I don't use it for much aside from that. I've used it on bass before, but I generally prefer using some sort of VST for bass recording instead of loading the buss up with built-in plugins.
Digidesign's AIR Distortion is a plug-in that is offered free in Pro Tools 8, the latest version of the industry standard audio recording software. In fact, there are a large number of AIR plug-ins available with the newest version of Pro Tools, so if you have Pro Tools and haven't done the upgrade yet, I'd definitely recommend doing so. There isn't anything that needs to be done in terms of installation of the Digidesign AIR Distortion plug-in beyond installing Pro Tools 8, as it takes care of installing all of the free plug-ins on it's own when you do so. The interface of this plug-in may be plain looking, but it makes it easy to get a quick grasp on it, which I think is the idea. In terms of parameters, it's got knobs for drive, output, mix, and mode. You've got hard, soft, and wrap to choose from in terms of mode, as well as a stereo button. In then has a section for tone with parameters for pre shape and high cut, and a section for clipping containing parameters for DC bias and threshold. I don't believe that they make a manual for this plug-in, but luckily one isn't necessary anyway.
I can't say that I've ever had a problem running this plug-in. I'm currently running it on a Mac Book Pro that has a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM. I run Pro Tools LE 8 with a Digi 002R audio interface or a Digidesign Micro Box depending on where I'm working from. While I haven't used this plug-in very much beyond initially trying it out, it isn't the type of plug that will take up too much processing power. If you're currently running some plug-ins in Pro Tools on your system without a problem, you'll definitely be able to run this one without a problem as well.
In general I'm not a fan of distortion plug-ins, so maybe I had a bias going into using the Digidesign AIR Distortion, but I just don't like the sound that it produces. I tried it on vocals, clean guitars, and bass guitar, and with all three I got a similar type of digitally scared sound. While there is a good amount of versatility and I do think that some people will find this useful, it just isn't for me. I always try getting my overdrive sounds from the source rather than a plug-in anyway. If you have Pro Tools 8 I'd definitely encourage you to try it and judge for yourself...