What I like in Acer: more responsive, better camera (with flash and AF), better screen (800x480), Quick GPS. On the Sony, the camera was really bad (no AF, no flash). The GPS was time to make the fix. On the Acer is literally immediate.
Another disadvantage of the Sony, it could happen to him to be literally "frozen" for several tens of seconds when he came out of his torpor. This T "& *% $ phone did not understand that I wanted to win when I received a call. Irritating.
Only disadvantages of Acer Z4:
1. The ring tones are not very strong, but I use the vibrator when I'm afraid not to hear an appeal.
2. The battery has less autonomy. However, there is an "economic" mode where all the stuff that consume (3G, backlight) are off or at minimum. In standby, and must hold out long enough, I think. Min 2-3 days.
3. The firmware is still a little buggy. To choose the ringtone for each SIM, choose a ringtone for voice calls: it is one that will sound for calls to SIM1 and another for video calling is the one for SIM2. Very intuitive. There are some other minor glitches. Globally, Acer did not seek to put a personal touch to the Android system, and that's good. The fact that works best and is all the lighter.
Why I do not like that manufacturers change the overlay? They sometimes have unfortunate initiatives. For example, for some reason, Sony had changed the clock, which suddenly no longer offers timer. It's stupid, but it is useful a timer. How do you make a boiled egg, otherwise?
To summarize, the Acer is a nice phone especially when it is offered around 90 euros. Quick to basic applications, GPS fast, camera with flash and AF, correct screen (for great in the corners, which can be troublesome to take pictures).
If Acer releases new firmware clean with small bugs fixed, I think I remonterais Note to 5 stars.