I am a proud owner of Xperia M since 2 years. Excellent build phone with smooth interface and voice clarity. Performance is good for itz specification and battery backup comes to around 14 hours when Data connection is ON for 24X7. Almost all required apps like whatsapp, viber, Instagram etc. runs smooth but Skype lags a bit. Skype is a real heavy apk.
The only drawback I see is in Camera. To be honest, the camera sucks! So, if you don’t care about using Xperia M for photography, you can buy this phone.