Correct, it spaces off the shoulder.
I got the trimmer yesterday and it appears to be very well made. I trimmed a few cases and it is extremely fast. Each case takes maybe 2-3 seconds to trim, so you spend more time picking up and setting down cases than you actually do trimming. I think once you really get into the groove you could easily do 10 or 15 cases a minute without trying too hard.
The trimmer is basically an end mill that chucks into your cordless drill, and there is a collar that slips over that and is held in place by 2 hex set screws. The collar has a bevel that matches the case shoulder, and the position of the collar on the shaft determines your trim length. It's a little bit of a pain to get the trim length where you want it - that's one of the few beefs I have with it. I used a case that was already the correct length as a gauge to set the collar.
Here's a picture to show what it looks like - I can't find my camera right now.
The trim is perfectly even and smooth. There are no burrs on the inside or outside of the neck, so if you were shooting boat tail bullets I don't think you would even need to chamfer. The cases will still need to be chamfered for flat bottomed bullets, though.
Trim lengths appear to be pretty consistent, usually within 1 or 2 thousandths of each other. I did run into one case that ended up about 7 thousandths longer than all the others. Since this trimmer spaces off the shoulder I'm guessing this was a case that didn't get sized down as far as the others, for some reason.
I do think that the hand holding the case will get pretty tired from gripping the cases after a while. I'm guessing a thin pair of grippy work gloves would help a lot.
Overall I'm pretty pleased. It's not a Giraud by any means, but it is ridiculously fast and a heck of a lot cheaper. Is it better than a Possum Hollow? I'm not sure, but its head and shoulders above the Lee trimmers.