I can't answer your question either but as the saying goes you get what you pay for. So at $15/pr I would say they won't last very long.
actually, according to the back of the package comparing those to the 30-35 dollar pair with lower 50-55 or so watts being 130% brighter having only 200 hours vs. 400 hours or so for these should be double the life expectancy at 1/2 the cost.
since I see by this post that some are using 85 watt on up, my guess is 67/60watt being these will not be too hot to melt stuff???