Well XPERIA U is famous for having
1gh Dual core processor
Colourful led bar
its compact size
In budget price
Secondary camera
But where it lacks is
512 Mb Ram - Major aspect which is considered in performance is low as we move towards higher ANDROID version it needs more ram
Multiapplication - Being 1gh dual core is not enough it can not multitask effectively at times it may cause freeze if many applications are opened at a time
Speaker - Speaker of the phone is very weak no one would expect it so many times u may miss the calls
Overall its a phone for those who use their phone lightly like little gaming few phones and txt messages