OverTone DSP Plugins have now been updated to V2.1.0. As of V2.1.x
Windows plug-ins are provided with signed installers, this provides a measure of security against unauthorized modification of the software and helps guarantee the software is genuine. Similarly, as of V2.0.x plug-ins for Mac OS X have been provided with gate-keeper signed installers.
From V2.1.x Mac plug-ins are 64Bit only, however earlier 32 and 64Bit versions are still available from the product download pages at
http://www.overtonedsp.co.uk/

For some reason that link takes me to a failed Facebook page. This one looks identical, but works...
 
http://www.overtonedsp.co.uk/
 
The 670 ($33) is the most interesting-looking product there.
 

The 670 is pretty good, and worth a demo, but I also really like their other compressors, the DYN500 and DYN4000.  The latter is an emulation of an SSL's dynamics section, complete with gate/expander. 
 
All the OverTone stuff is very good and very cheap.  Good combination.
 
Cheers,
Eddie