I grew up in Atlanta and when playing basketball in high school, I would sweat so much and drink so much water that my friends called me "moisture boy".  I could play ball for 20 or 30 minutes and I would look like I stood under a shower head with all my clothes on.  Fast-forward 15 years and 50 plus pounds, and I am still moisture boy, but I live in Colorado where it is usually pretty dry.  I like to mountain bike several times a week and was finding that the constant river of sweat out of my helmet and into my eyes and onto my sunglasses was one of my biggest discomforts with riding.  I bought a Halo earlier in the summer and now I never ride without it.  It works well as advertised under my helmet and fits comfortably.  My sunglasses are sweat free and my eyes stay clear *most* of the time.  On longer, hotter rides I wring out my Halo when I take a break, much to my wife's dismay.  I put it back on, and it is good for another half hour or so.  If I don't wring it out on longer rides I start to get some leakage, especially if I bend my head down (e.g. to tie my shoes or something) and lift it back up.

The bottom line for me is that I am a heavy sweater and the Halo is a home run and goes with me on every ride.  I have yet to test it in a humid environment like Atlanta, but based on my hottest and more humid rides here in Colorado, I think it would still be worth trying one in any environment.