I have a standard 2D Maglite with an incandescant bulb and also a 2D LED Maglite. I purchased the TerraLux upgrade to replace the standard bulb. The result is far superior to the old incansescant bulb, but when compared alongside the LED Maglite, it is not quite as bright.
As this upgrade is quite expensive, I have only given it three stars, since you can buy a new 2D LED Maglite for less than £25, so it is not amazing value for money, but does a decent job.