I got this on my last order to try it out and compare it to the original Sweet Watermelon since I have not been able to find any info on it. They smell and taste similar although you can tell the double is more potent. I always found CAP Watermelon to be a good flavor, but just a little flat and kind of dry. Adding Raspberry really helps the Watermelon POP if you will and the Marshmallow helps in adding some moistness. I whipped up a couple batches and enjoyed the one below the most:

Double Watermelon CAP 13%
Raspberry CAP 1% Can sub TFA Sweet Raspberry or FA here
Marshmallow TFA 1%

This can also be applied to the original Sweet Watermelon, you may just have to kick up the Watermelon 2-3%.