Originally Posted by Riyal
The built in screen protector of Sony in this device is already doing great for a protector. I say you should be more worried about the back side being scratched than the fron portion Also battery life you'll be overwhelmed by it's capacity to hold a single charge.
Not agreed with Riyal, if you are saying the Built in Screen Protector (Means the ASF Anti Shutter Film) then you are wrong, a lot of users from Z1 and Z1 Compact reported that the ASF scratch easily, attract dust and fingerprint.
Or maybe you are talking about the Screen underneath the ASF (by removing the ASF and lost the Sony Logo) then I don't know as I've not tried it yet.
Some users had a Screen Protector included in the Box (Depends on carrier and where you buy), then even the spare Screen Protector included in box are not good enough to prevent scratches and fingerprint.
Therefore, I would really recommend to get a decent protector for "Front" and "Back". Battery wise is good and last me more than 2 days of normal used. (My normal used consider FB, XDA, News Feeds, Browsing web, sync, email, whatsapp, Hangout, G+, Wifi, Mobile data, No GPS and other minor setting tweaks)