I love Bersa products (I carry sometimes a full size Thunder 40) but I would go with the Kel-Tec for even more concealability and more power.
For range use, the Thunder 380 is more appropriate, better balanced, better finishing, a more sedate round for the weight make it pleasant to shoot.
For the Kel-Tec I would get a P-11 over the PF-9, basically the size is the same, just a hair wider, is double stack (up to 12 rounds with flush magazines) and it has been around many years, a more proven design
I regularly carry a P-11 in my pocket, even in a business attire.
Again Kel-Tec pistols are not for extensive range use (even the company acknowledge that) as they can be uncomfortable, just enough to keep your proficiency with it.
Keep in mind that the 9 mm round is not only more powerful but on average is cheaper compared ot the .380
So my final advice would be go for the Kel-Tec if you do not plan a lot of range activity and just strict extreme (i.e. pants pocket) concealed use, Bersa if you want to shoot often.
However Bersa offers a compact version of its full size Thunder pistols, chambered in 9, .40 and .45, however they are bigger than the Thunder 380...so not really pocketable handguns.