(1) Fit is important, OEM is best. You do realize that A LOT of cutting will have to be done to the car to fit the 90mm in there, UNLESS they push the actual lighting assembly out farther.
(2) 90mm Hella is best, what bulb assemblies will be accepted? H7, H9, etc.?
(3) SEAL. If these can be OEM sealed, AWESOME.
(4) PRICE. $350 is dirt cheap for a lighting assembly like that INCLUDING the Hella's.
I have MM Xenons, love them to death, and they work fabulously ONCE I sealed everything, but that was a trial and error thing.
Here's an idea of what fitment with the hella's in low and high look like:
As for buying tons of sets, I'm sure EVERY 98+ would buy them here if they're at $350 per light, because OEM are $250 per light (so ~$500 total OEM vs. ~$700 for these).
