I had a bad experience with them, I'm afraid. For one thing, they do not custom-make dresses to your measurements as they claimthey take a dress that is a size too small and let out the seams to accommodate your figure. Not only is this method hit-or-miss, it means there's not a lot a tailor can do to fix the dress if you need more room.
Also, the quality of the dress was nothing like the photo. The beading was cheap-looking and poorly done, with little threads sticking out and glue showing.
You'd never know this stuff from the user reviews on the site because they take down all the negative reviews. They wouldn't let me ship the dress back to China for a full refund, so they just gave me a partial refund and told me to keep it.
I do see the appeal in paying less for something you'll only wear once and will probably look OK in photos, if not up close. But I would say that Light in the Box probably works best if you are an easy-to-fit size and you pick a dress that doesn't have intricate details or complicated construction.