Conclusion: The Speedlite 270EX II does a fine job when used on-camera, but the slave feature is only marginally useful. Because having to aim the flash head toward the mastter (in my case, this is my Rebel T3i camera) in order for it to receive the signal emitted by camera's built-in flash, defeats the purpose of slave operation. Canon should have positioned the sensor on the 270EX II in a more omnidirectional location in the Speedlite.
Pros: quiet, Good Exposure performance, Superior build quality
Cons: Slow recycling time, difficult to use as a slave
Conclusion: I used this on a 5Dmkii while visiting South America - the 270EXii was greta for indoor family photos with bounce flash and great for fill-flash outdoors. Small, two batteries, exposures were excellent.
Pros: Good Exposure performance, Superior build quality, Fast recycling time
Conclusion: I bought this flash as a fill in flash for travel. I do not use flash a lot - my Canon 5D Mark III has very high ISO range. But sometimes it helps. The build is solid, the control is simple. In case of Mark III you can fully control the flash from the camera - put in manual mode (1-1/64), slow sync, etc. Most of the typical features for Speedlight flash. Another feature I found useful I can use this flash as a remote control for my camera.