To my knowledge Mag-lite had a big panties in a bunch patent on the cylinder body (isn't this like putting a patent on the circle?) so over a law suit Inova re-designed their flashlight. I may be wrong, but thats what I assume happened.
The flashlightreviews.com one is the older version with the recesses on the body. The flat sides design is the new one. Is there a differenc ein output? Maybe very slight, with the new LED's coming out and all (26K, 35K, CS, MJ, and all the other 5mm LED's.)
If you need a durable, fairly inexpensive, ~10-15 lumen light that will suck batteries dry, the X5 is nice. I put some RCR123's in there (~4.2v each, so max voltage going in is 8.4, NOT recommended.) I just wanted to see if it would work, and it did at a brighter level but at the cost of damage/premature death to the LED's.
There are other options out there though, just depends on what you need it for. My fear with Inova is cross threading the tailcaps on them, and the lack there of in output (not a slouch either, kicks more cheap incandescents.)