The Lumintop TD15X looks the same as the TD15, but the CREE XM-L LED in it instead of the XP-G in the TD15 makes a huge difference to the beam of the light. The XM-L (TD15X) gives a nice, wide, floody beam that will light up a wide area at once where the XP-G (TD15) is very focused, with great throw, but a very tight beam. The multiple modes are still there, so you have quick access to three outputs and strobe by loosening and tightening the head.
One of the cool features of the TD15 and TD15X is that you can add extenders on that will add the capacity for 1 CR123 at a time or two for an 18650. The output does not really increase, but the runtime can get crazy long as you add on extra cells.
Here is a super exciting (maybe a slight exaggeration) video that shows the two models in comparison to each other: