1/18/2018 Update: I changed my rating to five stars, after confirming that the new Petzl Trigrest does fit the shaft between the bottom ferrule and the top of the rubberized grip.
Bring a Trigrest and an appropriately sized allen key, and this axe will also be great for sustained 90 degree steps.
I recently purchased the 52cm version and have used it a few times. I am 5'10". I bought this with the intention of using it with a second "50cm" ice tool on steeper terrain.
My first impressions are that this axe appears to do everything (self arrest, self belay, plunging, daggering, chopping, building T-slot anchors, piolet traction on less than vertical terrain) well and is comfortable to hold in all normally used positions. The pick, adze, shaft, and spike all are well-designed and work well. However, it should be noted that the shaft and pick are not "T-rated", so it would be prudent to avoid really aggressive torquing.
The spike sacrifices a little bit of functionality in firm snow conditions for weight reduction, relative to other fully tapered steel spike designs on the market. However, most people will not notice or care about this particular compromise.
I was told by a Petzl rep that the Summit Evo is "not compatible: removable trig rest made by Petzl. In my opinion, adding a removable sliding hand-rest (see Sum'tec and recently revised Venom for examples) would have made this axe more functional for leashless, sustained vertical climbing. If this feature is added (at least for the lower part of the shaft), I would revise my rating to 5 stars. That being said, you can add a leash for wrist support while climbing vertical terrain.
In summary, this axe excels on terrain from about 40 degrees to about 70 degrees. It is adequate for short steps of more vertical climbing, when paired with another tool. It is outclassed by axes with removable/ sliding hand rests for sustained vertical and overhanging terrain. It is adequate as a standalone axe for terrain less than 40 degrees, but there are cheaper alternatives that are just as good or better for lower angle terrain.