I think they did a good job to be honest. The BKA (with the help of RUC and BSSO/MI5) pretty quickly identified where they might attack, who they were looking for and how they might catch them (they developed software that tracked suspect looking car rentals for example as the ASUs rented vehicles all the time – a couple of times the BKA nearly got them too. That forced the IRA to concentrate on buying / nicking cars instead) The BKA found weapons dumps and staked them out, preventing the unit from coming back to retrieve Semtex and weapons. The German police did some pretty clever and sneaky stuff, which I am not allowed to reveal but they basically forced the IRA into changing their plans constantly. But due to resource limitations, they couldn’t be everywhere at once, so sadly attacks like at Wildenrath, Unna, Hannover etc, couldn’t be prevented - but that is the nature of terrorism unfortunately. As the IRA themselves said “you have to be lucky every time, we only have to be lucky once.”
As a side note though: although the Germans worked really closely with RMP & RAFP and BSSO, there was a lot more that London knew about what the ASUs were up to, that wasn’t passed down along the chain to the Germans, which would have helped them prevent certain events from happening. Complicated issue.