Kel Tec P3AT - .77 inch, 7.7 oz
Beretta Pico - .725 inch, 11.5 oz
Got both.
While the Pico is thinner, it is almost 50% heavier than the P3AT. There is a noticeable difference in weight.
The Pico has real sights that can also be upgraded to real night sights. There's also an available grip module that has an integral red laser that can switch between pulse and solid dot. The downside is that it can sometimes be activated if you back pocket carry. The Pico is also DAO which means you got double-strike capability in the event of a misfire or failure to fire. The mag release is weird. It is neither traditional US style release nor European heal release. One pulls down on a US style positioned release instead of pressing a button. One handed mag release can be done but will need practice.
The P3AT is lighter, but has practically zero sights. It doesn't feel as solid for obvious reasons. I have a Crimson Trace trigger guard laser on mine. So, weight wise, it is on par with the Pico. Mag release is traditional US style. It is also one of its weak areas. The mag release is plastic, whereas the magazines are steel. The mag release has a tendency to wear out and the mag will lock at the lower and lower level unless you practice holding down the mag release during insertion and release to extend its life. The other option is to swap out the mag release to a steel version. The drawback is that you will likely have to file a tiny bit of the frame around the mag release housing to get good fitment. Trigger is partial reset DAO.
Overall, the Pico is a more solidly built gun. I like it for the sights, real DAO, and integral laser grips. However, I carry the P3AT more often. I back pocket carry and the Pico's laser has been known to turn on. It's actually a simple fix if I wanted to spend a little time on the pocket holster but I'm lazy.