In general, any teleconverter for any camera will do three or four things:
1. extend the length of the lens by the magnification factor (like 2 times in this case).
2. degrade to some extent the image quality of the original lens. This is because t/c's whether high quality or not, are not going to be as good as a lens designed to function in a specific way.
3. will loose some f-stops on the original lens, I don't have a good explanation for that, but that is a side effect.
4. very likely change the functionality of the lens (like loosing the AF functions of the lens or eliminating the lens information connection to the camera).
Anyway, that's what one may expect with t/c's in general. I don't know this specific t/c but if it's like this one
Rear Converter-A 645 2X Lens Reviews - Pentax Lens Reviews & Pentax Lens Database, I'd expect that you will get the magnification you want but at some degraded image quality over that of a dedicated lens at the equivalent length. T/c's are useful IMHO, and I carry one (a 1.5x) for my k-mount cameras in my photo bag for times when I want more reach. It gives me that but it's not ever as good as a dedicated lens as I've said.