I've bought this lens because I was not satisfied by the 50 1.8.
This one is better in every aspect:
- Much better AF (noisier but much more accurate, even in low light)
- Very sharp even wide open
- Better contruction
- More useful focal on a 1.6 crop camera
On a 400D, this is a near perfect normal lens, very light and compact.
Excellent IQ for a little price.