Thanks for the clarification and descriptions. In general, it sounds like it might be more difficult to train successfully in agility / obedience, etc (just not bitework) with a younger DDR dog compared to a WGWL or Czech dog?
It will depend upon the dog, whether the dog is "DDR", WGWL, Czech or a mix of the lines. Not all dogs from the bloodlines are the same. Furthermore, bear in mind that many of the people reporting in above have stated that their dogs are a mix of DDR and Czech or DDR, Czech, and WGWL. So what line is it that makes the particular dog what it is? Is it the "DDR"? The Czech? Something else? I am not being critical, I am simply suggesting that using generalities about lines or extrapolating individual experiences as being representative of lines may not be the best way to go about finding a dog that suits you.
I have both a 4 year old female from east german ("DDR") lines and a young male from what would be considered WGWL (although there is some old DDR, Czech, etc) back in the pedigree). My "DDR" dog was not slow to mature mentally or physically (although she has not been worked in protection). Moreover, she does not have low prey drive; it's not on the level as my WGWL, but it certainly is not low. She is very smart and a quick study, even at an early age. Easy to teach motivationally with toy rewards and an inexhaustible desire to hunt. With that said, her knowing what she is supposed to do and actually doing it are sometimes two different things. She has an independent streak a mile wide, often has her own agenda, and would rather beg forgiveness than ask permission. If you have what she wants you are golden; if she wants something that you do not have more, well, buckle your seat belt. She has many great qualities, but I would not include biddability on that list.
In contrast, although my WGWL line male is higher drive and more serious, he is, overall, an "easier" dog to handle. Whereas my "DDR" female often has her own agenda and will blow you off to carry it out, the WGWL male's life revolves around interacting with you and trying to anticipate what you want. His ears are always open, even when in a high state of drive. Moreover, he has higher thresholds and is much less touched by things going on around him. There are other differences, but this is one of the major ones.
In noting the above, I am not suggesting that my experiences can be extrapolated to "DDR" vs. WGWL - this is just a couple notes on my particular experience, and I am far from being an expert.