I own both of these and, while I do enjoy shooting both and they are both very accurate etc, I would not trust either with my life. My Bersa thunder has the trigger spring issue and has occasional failures to fire and my Walther is, not only a .22, but a very unreliable one.
They are comparable in size but, IMO, the Walter has the more comfortable grip and feel. I do have small hands but, to me, it feels more like a real gun and, since it is a .22, there is virtually no recoil. The Bersa, on the other hand, has a shorter grip and does have some recoil. Even being a .380, the thing doesn't weigh much.