Gosh, TonyL, that is a detailed reply - thank you. To answer your question, it should be an all rounder - both for targets and for vermin.
I am sorry to learn that Diana has quality control issues these days. They have a great pedigree and produced the wonderful Original 45 40 years ago - still a rifle somewhere at the top of most collectors' lists.
Most underlevers seems to have an anti-bear trap device. I suppose my preference is break-barrel.
I was put off Walther after reading, on the forum, that the transfer port was too narrow and that, consequently, pressure was placed on the spring after a few hundred shots. There was quite some discussion over this.