My 18L is awesome. It took me a while to get to that wheel, as I started off very slow and kept upgrading.
It weighs around 46#, less than #50.
If you want something under 50#, I don't think there is any other good option. The higher power of the 18L is noticeable, compared to the V10F (I have both). The V10F is a little more nimble and has higher pedals. I still like having my V10F as my back-up wheel, but my 18L is a beast. Both have LEDs and good sound. I would say if you want slightly higher pedals and don't need all the power, the V10F is the way to go. If you want to experience really good power in a small package, the 18L does the trick.
I still ride my 18L more than my V10F, as I did a 30 min ride at near max speed and it started giving out. My 18L seems to last a bit longer on hard rides.
As others pointed out the 18XL is the upgraded version of the 18L, but yes...it is slightly heavier.