Define sufficient. All skimmers clean the water to an extent. The more air and water drawn in and mixed together along with how fine the bubbles are chopped makes one skimmer better than the next. Not to mention how much electric they use. That may or may not be part of the equation...depending on you.
That said, i've used a few of those ASM G series skimmers throughout the years and I have found much more efficient skimmers.
Ultimately, a G2 is nowhere near enough skimmer for a 240 gallon with a sump in my opinion. I had a G4x on my old 195, and I thought that was a bit underpowered.