The G2 lets 30% more power through, just feel how hot that 3 element gets in about 5 seconds. The 3 element also clips the ends of the line.
What you want to do is use the G2 or a G7 and a SANWU 3X expander, it makes a world of difference.
A nubm44 with a G2 and a SANWU 3X expander is fun, you get about a 1 inch long line at 20 feet but you can focus it razor thin and burn the heck out of stuff.
The G7 is a single element with a longer focal length that makes a 3 element size line with more power, add the 3X expander and you will love it.
For desktop or home CNC the G2 is what you want, but for out in the yard at 15-20 feet you want the G7 and 3X. The G2 and 3X has some reach as well.
The 3 element will work, but you lose power and build heat faster, that reduces runtime.
With a 7875 I say the heck with it and use the 3 element, but with the 44 you can see the extra power, 30% of 3 watts vs 30% of 7 watts makes enough of a difference.
The G7 and 3X will out range the 3 element for burning easily.
SANWU
Here's a comparison between the 3 element and the G2, notice how the heat build up with the 3 element causes power drop from faster heat build up.
http://laserpointerforums.com/f65/nubm44-6w-450nm-laser-diode-94119-18.html#post1370058 <<<Click the link