Yes it worth buying, even in 2019, it's a pretty decent phone with high-end performance.
The Z3 compact is a pocket phone, it's small, discrete and stylish. The Z3 is completely waterproof.
The camera is outstanding, but you do have to get it out of Auto and put the .iso down to 50 or 100
There is built in noise canceling, missing from most phones.
The screen is an IPS, meaning you can view it from many angles, not just directly in front of you.
Battery life isn't just about the size of the battery. The power efficiency of its various
components and software optimizations all play a role.

Battery is. amazing, speed is awesome and Android is just so much better than iOS.
Just updated to lollipop add well and It's perfect with the z3.
The right hand side hosts the power button midway down and the volume rocker just under that.
Right at the bottom of the right hand side you’ll find the dedicated camera button
for when you need to quickly take a snap.

Sony’s Xperia Z1 Compact launched with a 4.3in display whilst the Z3 Compact has now expanded it to 4.6in.
Personally I find this display size pretty bang on the mark; it offers a good size for viewing media
whilst sitting comfortably in the palm of the hand without having to use
two hands to reach the top of the screen.

Sony has managed to pack in a top-of-the-range processor with a powerful set up – in fact it is exactly
the same as what you'll find aboard the Xperia Z3.
It’s an MSM8974AC Qualcomm Snapdragon 801 quad-core processor. Those four cores are using Qualcomm's
Krait 400 architecture which has been clocked at 2.5GHz.
There is also an Adreno 330 graphics processing unit (GPU)
on board with 2GB of RAM on top of that.

The small phone that does it all.