When u purchase a HID conversion kit, will u consider the brand? For me, NO. As i believe, 90% [if no 100%] of the kit is make from China now. The seller only rebadge with their own brand. If u want to talk about branded HID, Philips is the one of the famous. The real Philips product may cost u more than 1K.
Jarance, i have no experience with HB4 bulb on e39 headlight. Anyway i guess they are all the same work to retrofit into the headlight.