Some guns define the manufacturer.
Bersa is known for the Thunder .380.
Kel-Tec is known for the P-3AT.
Unfortunately, like an actor who has one long lived wildly successful role, these companies have been stereotyped by their most popular product. They are victims of their own success. When you want a deep cover, small .380 CCW these are the products that make the list. But when you need a more serious service pistol, you look elsewhere.
Are their products any good in larger calibers? I wouldn't know. I don't know anyone who has one. But if you need a small .380....