I have and carry both. The action on mine are both about the same. The Scarab has an open frame with vents on the front and rear of the knife. I don't really know why it has these, but maybe it's a cleaning feature of the knife or fire under water or something. In reality it makes the knife fill up with pocket lint faster and will start to fire shitty. Make no mistake, this happens on both knifes, but just faster on the Scarab because of the holes on the front and rear of the knife. Both knives are easy to clean, but the Scarab uses common headed screws and the Troodon uses specialty screws with a proprietary head so you need the special bit for disassembly. Get whichever knife speaks to you. You will probably end up with both in the future anyway.
Also, I have a Scarab II with a double edge full serrated blade incoming this week.