43 to 45 cm backrest is considered, at least by me, an AVERAGE height of a seat back. That means it is GOOD, as on twin/double strollers, seatbacks are ofter even below-average, height-wise. If the canopy is not immediately above the end of the seatback, it is an OK height.
From your two choices, I would absolutely go for the Joie Aire Twin. It is simpler, meaning also more compact, and I personally don't like the Hauck strollers' quality (it is made quite cheaply. However, count on the Joie to not be very all-terrain, it is an urban double pushchair.