I have a G3 and it skims well. I do have a few issues with it though. First you need to keep an eye on it, as it will need adjusting. When the neck gets coated with gunk you need to raise the water level a little with the riser tube to keep it skimming effectively. I would recommend getting the gate valve modification, makes adjusting much easier. Second, make sure the skimmer will be in an area of your sump that has a constant water level, if you have room to set it up in a separate sump, say a 10 gallon, that would help. If the level in the sump rises for any reason, it has the same effect on the skimmer as raising the riser tube, and may cause it to overflow. Neither of these issues are deal breakers IMO, just a heads up for you!
PK