So far I did not like the flash and have therefore always set to bright fixed focal lengths and more screwed to the ISO values when using the internal pop-up flash of my old 40D. If it was now even with higher ISO values and a bright lens no longer possible to take a relatively sharp image, so I then in an absolute emergency but still quite important for the internal flash to capture at least the memory. I was satisfied with these results, never, but better than no picture!
Now that I have sold my 40D and a full-scale 5D M2 (Thanks to falling prices for the successor M3) I switched, I was not an internal flash longer available. Combines high ISO values that the 5D M2 without much noise and even tolerate my good fixed focal lengths, I wanted to completely abandon flash.
Unfortunately you do not always drags all his lenses around with you, so every now and then is just the immerdrauf lens available. In my case, the 24-105mm IS USM 1: 4L, which is not exactly known for its light intensity. Then she is suddenly there, the situation with little light and no flash, which would allow a least detain beautiful remembrance. Then it will even work closely with high ISO values, should not the natural or artificial room light be sufficient.
My view, therefore, went to this shoe mount flash. After reading some reviews and various community contributions and after I weighed between the 430EX II and 580EX II, I ordered despite my reservations about this flash. What can I say, I am extremely positively surprised. I was completely unaware of what is possible with a high quality flash. The motive can be benkenlos so subtly brighten people to think while looking at the image, it was not a flash was used. The many options and a bounce flash enables pictures with creating unprecedented (for me) options.
Hence my recommendation: Do not be put off you from the internal flash, because there are worlds, actually more galaxies between an internal flash, and this professional flash system ...