The first thing you notice is the amazing display. Looks like blood dripping over icebergs. The dripping red indicates the volume being squeezed off the peaks. You can even roughly "tune" the limiter by aiming to get the reduction (red) to neatly fit the peak (light blue). The attack and release correspond well to the display, but I couldn't notice any visual representation of the lookahead. I can hear changes as I move the dial but can't notice anything on the display. Guess I shouldn't ask for too much.
The operation can be divided into two stages. Firstly the transients are detected and squashed according to the lookahead and "style" values. Then the limiter applies "attack" and release to the result. Calling this first part of the envelope "attack" is unnecessarily confusing. It would probably be better to call it "hold" or "delay". Measuring the attack in seconds is also pretty confusing at first. Thankfully the display gives you a good idea of what is going on.
There's also the option of separating the channels (0-100%) for both stages of the limiter. I haven't explored this feature yet. It's making my head hurt just thinking about it.
The "style" variations do genuinely sound quite different, especially at high gain settings. With all the options it's hard to imagine not being able to get a good sound out of the Pro-L. You might find you can comfortably squash 10db off your tracks with this thing.
What else can I say?
It's got oversampling. It's got dithering and something called ISP which you probably don't need.