It's 38 degrees for FWHM (Full Width Half Maximum, I assume as they did not specify). That means half the output is wider than 17 degrees either side of straight ahead or up and down. I ride an 18-20 degree FWHM low beam on the road and it is floodier than I'd like and am considering reworking its lenses. It is not just the width going off to the sides but the washing out of the strength of the beam over the wider output and sending a lot of light up into tree branches or to make a hot spot in front of the bike.
Getting the large dies of the MC-E to provide something approaching a narrow 10 degree spot beam requires fairly large reflectors, and they won't fit the MR16 shell. So this may be as good as it gets for an MC-E in an MR16 package.
Then there is the color. Warm white may help discern root and other road and path issues better, but the highest output bin is 75% of the output of the highest output Cool White. A neutral white might be a better compromise of color versus output. YMMV. Color preference is a personnal thing.
If all four dies are driven in series then 6 watts means they are underdriving the LED at about 500 mA. Likely kept low to aid cooling in a static situation like a room. About 340-400 lumens out the front depending on which bin was used (likey the cheaper lower output one). In the right beam, 300+ lumens would be decent.
DIY is about doing and learning, my first was a 1 watt 100 lumen MR16 10 degree spot. Too little power, nice beam, decent color. So you may wish to build it to learn.
