The Massey Plugins THC Distortion is a unique sounding distortion plug-in that is available as an almost fully functional demo on the Massey website. I have not bought this plug-in but I use this demo version - the only limitations are that you can't bypass the plug-in or save any of your settings; every time you re-open a session the plug-in will set itself to default. I usually just write down the settings in Pro Tools, but sometimes I do forget that the settings need to be reset. The interface of the software is quite easy to follow as it simply has parameters for drive, filter, and level. It also has a meter and has the look of a stomp box. I've never seen the manual for this plug-in so I don't really know if it would be helpful, but the plug-in is extremely simple and I would imagine that most users won't need it.
I generally only use the Massey Plugins THC Distortion one or two at I time as I just don't use all that much in the box distortion. For this type of use it works fine and I would think that you could probably even run a bunch of these at a time since they don't take up too much processing power, but since I've never done it I can't say for sure. I've been using the plug-in for about a year or so, but I use it pretty sparingly.
Even though I probably wouldn't have this plug-in if it were not for the free demo that is available, that isn't because I don't like the sound of this plug-in. It does have a pretty raw vibe and is pretty realistic as far as plug-ins go, but I just don't use that much distortion that I don't have coming out of an amp. When I do use it I mostly use it for vocals and I believe that it is best for that rather than for using on a guitar unless you are looking for a more subtle effect. The price of the Massey Plugins THC Distortion is the best part as the demo is free and the normal version is quite cheap as well. Overall, the Massey Plugins THC Distortion is a great deal and is definitely worth checking out.