They cannot be used together.
I am not aware of anyone making a +1 bersa style extension. I would buy a couple if they were available.
I like the +1 with a hogue handall jr. The +1 by itself didn't help the grip feel as much as I thought it would. Once I added the hogue sleeve with backstrap padding under it, the little sucker became a dream to shoot. If I pocket carry, a regular mag is what I prefer. Less to snag on. YMMV