I'm getting the G5 for my 200g+ upgrade next year.
I have a G3 on my 75g reef (stocked on the heavy side) right now and absolutely love it. The skimmate that collects on the neck is the consistency of thick oatmeal. With this skimmer and weekly water changes, my nitrate/phosphate levels are minimal. Also, I haven't done any adjustments to it since I broke it in almost a year ago.
Maybe the MSX and Octopus are better, but I figure why take a chance if I know the ASMs work so well.
Pictures below show about 36 hrs of skimmate production by the G3: