What are LiFe Batteries and are they Worth the Tamiya Tax?

LiFe is a battery type popularized by Tamiya in the radio control vehicle world, especially in Japan, and seems to be a middle ground between MiNH and LiPo RC batteries. Is it really even safer and more flexible than MiNHs? Is it really safer and lasts longer than LiPos? Is it worth the Tamiya Tax of purchasing one of their LiFes from them, or is it better to buy from the third party aftermarket instead?