I wouldn't have doubts about the quality of the Hella projectors, can't say the same for the aftermarket HID kit though since I've had weird experiences in the past.
If you plan on getting new Hellas plus an HID kit, you might also want to look for used OEM xenons that include the headlight assembly, bulbs and ballasts, but then you would also need an adapter (~40 GBP) and someone to code them. I believe there is a set for sale in the classifieds.
You would also lose height adjustment unless you install the OEM module with the sensors. However, you will have the bi-xenon function that Hellas lack.