HBE says that the CPR (ComPressor Retro) is modelled after a vintage compressor circuit... but it's not saying which one.
Controls are fairly standard, with a sustain knob turning up the compression and the level knob setting the appropriate output, with enough on tap for a neat boost function - with or without the sustain knob turned up.
The attack knob sets how quickly the compressor kicks in on your signal, allowing you to shape the front-end of your note envelope to suit the musical context - that Nashville snap being there if you want it.
We find the CPR does all the things you'd expect from a good compressor - keeping the sound tight and focused, adding definition and helping squeeze out the sustain.
There are plenty of good pedal compressors, and the CPR joins the ranks; it might not appeal to those wanting to conserve space on their 'board, but it'll certainly look good on it.