Both are brilliantly engineered devices. I don't have the GG Ithaka, but I do have the RH Hercules. They put out massive amounts of flavor and are almost like dripping with a tank.
They both have their flaws as well. I only have the Kayfun Lite. The draw is a bit airy and with the Lite, you cannot adjust it. You can with the KF 3.1. Also, it would be nice if Svoemesto would have included an extra post for DC.
The Ithaka/Hercules require NR wire for the build. This is a bit of a hassle, but like anything with RBAs, after you get past the learning curve, not that big of a deal. I have just been using the 'ready wire' that different vendors are selling. It makes the build a lot better.
Lastly, both of these guys are a total pain to refill. You either have to wait until they are bone dry or spill e juice.