Don't know where or why you get this from. It's a pretty straightforward country to fly into/through. ATC are very professional and friendly, most airfields I ever have been to were well organized and some even have (or at least had) excellent restaurants
As you say you\ll be in a twin, I guess at this time of year you'll going IFR, if not, then be advised that the old VFR transponder settings have gone, it's standard now, although you will get a squawk anyway.
What might help (I don't know Essen/Mühlheim) is to call immediately before departure with an ETA. This definitely worked in Siegerland, where the fire brigade used to do the immigration checks ! Suggest you give them a quick call to find out if anything special is required.