I just received a Twitch 2 and a Scallion and I must say they are both very impressive little knives. Fit and finish are excellent on both. Both have great looking aluminum scales. I chose a blue Scallion and a gray Twitch 2 but they each come in a number of colors. The Twitch is a bit slimmer and has an industrial look to it. While the Scallion is curvy and a bit more artsy. The Scallion's handle is listed as 3.25" and the Twitch at 3.5" but they eyeball up pretty much the same.
Both have non-reversible clips that (IMO) look nicer than your standard Spyderco clips. Scallion is tip down, Twitch 2 is tip up. The Scallion's clip is a longer and is really tight. This knife will not accidentally come loose when clipped to a pocket. Both have lanyard holes. For some reason I was under impression that they were made in Japan or Taiwan. I was pleasantly surprised to discover that both are USA made.
Both knives seem to spring out with about the same energy. It is best to use the flipper on both. The thumb studs seem to be cosmetic on the Twitch 2 and act as stop pins on the Scallion. It is pretty easy to slice your thumb if the studs are used. If you have used thumb opening devices on knives before, it is a natural reaction for your thumb to try to keep up with the stud. The blade will most certainly be faster than your thumb and you might end up with your thumb pushing up against the blade.

When opening the Scallion, if you leave your finger in the upper portion of the thumb rest area you may prevent the lock from fully engaging. This is because a grooved portion of the blade spine rises a bit above the back of the handle and acts as thumb traction. This is not a problem with the Twitch.
The safety switch on the Twitch is well engineered. The knife can be locked closed or even safety locked open. The Scallion safety switch is simply a plastic bar which blocks the tip of the blade and prevents it from swinging open. The Scallion is a liner lock but it seems very solid. I have no blade play in mine. As long as I hear it "clack" and know the lock is fully engaged, I have no doubts the lock will hold under usage. The Twitch is a lock back with a "pass through" lock bar, very ingenious. This makes it possible for the Twitch to have a flipper and still be a lock back. The Scallion gets a bit more play time because it's liner lock is better suited to one hand open and close. I'm sure someone with a bit more creativity and/or manual dexterity than me has figured out how to one hand a Twitch.
The Scallion's blade is listed as 2.25" 420HC and the Twitch 2's at 2.6" AUS8. The Scallion has a slight re-curve which will probably give me problems when I try to sharpen it. The Twitch 2's blade is standard drop point and is a bit longer, thinner, and narrower. The Twitch 2 performed a bit better out of the box in slicing up a Post-It. I selected plain edge for both knives but I think they both come in combo edges as well.
Both knives are great. I couldn't decide between the two so I got both.
