I have said this before, but IMO, the majority of GSDs sold as DDR or Czech have little in common with the original DDR/Czech dogs such as the former Pohranici Straze kennel/lines. They have been diluted and their appeal is their bone and pigment. They were originally known for being very aggressive, dominant and independent, and not necessarily that prey driven. I don't buy that they take longer to mature. I'd argue that people are waiting to see more prey drive from these lines and it often isn't there to the degree of an extreme West German workingline dog's prey drive. The old lines are gone and now you often have these lines that are marketed as something they are not. There are some people still breeding solid Czech lines, but even kennels like Eurosport k-9 in Slovakia crossbreed with West German working lines to get a sportier dog.
The problem with training a dog in sport and then converting it to a protection dog, is that you make it harder for the dog to truely protect because there is so much early emphasis/training on obedience at an early age and the dog learns to see the helper as a someone to play a game with rather than a real threat. It really depends on the genetics of the dog. But most people into protection sports want to start training their dog from a young puppy, especially introducing rag work, tug, etc.
Also, a lot of the West German working lines have what Helmut Raiser calls hypertrophic prey drive, which is lacking in other aspects of aggression.