The Bottom Line: Overall it's a superb mountaineering tool, and I would highly recommend it for anyone looking for a general mountaineering axe. I certainly think the minor improvements add up, and make for a better tool that is totally worth the extra cost. For routes like Fisher Chimney, Silverhorn, Coleman-Denning, DC it's a great tool for a variety of applications.
I've been using the Petzl Summit 2 for a couple of years now. In all my retail experience selling ice axes, I generally tell people not too worry to much. Differences in ice axes are pretty minor, and they are going to accomplish the same tasks. With that said, I did have a few little things in mind when I was purchasing my axe. My previous ice axe had been an older DMM Cirque 59 centimeter. I found the rubber handle accumulated snow, and the length, while technically the correct size for me, was too short for probing possible crevasses. While tempted by the Summit pro I thought the hydroformed shaft wasn't really any more useful, and I was avoiding rubber grips. I have used Black Diamond Raven's and always found them awkward to hold. I really like Grivel axes, but I didn't have a pro deal with them.
So the Summit was my choice. I have since used the summit on many, many peaks, mostly in the Canadian Rockies and BC Coast Range. I've been on everything from deep powder couloire ascents to 45-degree glacial ice slopes, crunchy neve couloir, and snow-covered rocks where the odd hook and torque move came in handy.
The Summit 2 has a superb design. The stainless steel head and spike are solid, and they keep their sharpeness well (too well, as my sleeping mat just discovered). The offset shaft is smooth down to grooves for a better grip near the base. The weight is 400 grams for the 66 centimeter, which is pretty darn light for an axe of this size.
I've never found much difference between ice axes when arresting. To my mind, only the length seems to alter the performance while sliding. I do like how the a piolet grip on the axe is most comfortable in the ideal arrest position, so the one time when I was caught off guard and had to arrest, my hand was ideally situated.
Daggering and plunging is where the Summit shines. Being offset, there is a bit of space so you aren't burying your hands when daggering. The smooth grip and slight curve on the head is so much more comfortable than flat or edges, so your hand won't be aching hundreds of plunges later. Honestly, this is the feature that stands out the most. Your hand just kinda slides perfectly onto the head.
On steeper ground the Summit is decent, but no worse than any other mountaineering axe. It doesn't have much weight in the head, so it requires a forceful swing, especially on glacial ice. I've found the Sum'tec and even the Raven have a little more heft in the head, but the Summit's offset shaft does make it more comfortable to hang on to, and it keeps the hand a little removed from the ice, allowing for a more powerful swing without fear of bashing your knuckles as much (compared to the Raven). I have added a quark trigger rest to mine. I would definitely recommend this if you are planning on getting on anything steep. We encountered a sustained surprise ice patch on the Silverhorn on Mount Athabasca in 2016, and having a trig rest made the 45-degree ice climbing with only one tool much easier. The grip grooves alone aren't that useful for grip.
The place I do feel the Summit suffers is chopping steps. It seems to struggle a bit despite the adze being angled accordingly. I don't chop steps that often, so it hasn't really affected me.