My biggest problem with the LC100 is the bulb/ballast vulnerability. I lost $80 because the bulb died on me while the light rolled off of my closet chest (3 feet high) and onto the floor (carpeted and insulated floor, at that)... For the cost, it's outrageous how brittle the bulb is.
Now the X990 is a completely different story. While opening my car up, I had placed the X990 on top of my car's roof. Well, being that it isn't a flat road, the X990 tipped and dropped from the roof of the car to the ground, bounced around a couple of times, and had a few scratches to its yellow lens lip, the aluminum head and the battery body... Turns on and performs just as good as the day it came in the mail; quite a different experience than the LC100...
That's my problem with the LC100...