I have owned them all..I had the Aphex 230, and didn't like it because the "gate" is too "gate-like" It acts more like a switch and either is on or it;s off..no ramping up like an expander..Also the APHEX pre-amp sounded "grainy" to me..several clients told me it sounded "harsh".
The Symmetrix boxes all seem to have the expander AFTER the compressor, and that casues the "whooshes" at the end of sentanses or phrases. The Focusrite boxes all sound pretty good, but be careful of the power supplies in some of them.
For now the box of choice for me is the AirCorp model 500TV..not the grey-faced 500PH (although that is an excellent box) The TV model has an adjustable release time control that smoothes out the processor for the tastes of the TV production people that kept telling me to run with NO processor..
Available from Air Corp.