The biggest drawback I've found thus far is cleanup. My old system required about 10-15 minutes from the time the wort was in the fridge to the time is was packed away. But that's on the driveway, with a garden hose. The GF requires more delicate touch, and a good bit of recirculation.
Which leads me to another potential drawback--having been designed around the water saving brew-in-a-bag system, this thing does require a lot of water to recirculate for chilling and cleaning, not to mention reheating. It's not a concern for me, but if water and time savings are a priority, it could be seen as a drawback for some.
My old system was about a 30 minute clean. Seems to be the same for this one.
I didn't view the GF as having been designed around a water saving system, but rather one with a very small footprint. It takes up considerably less space than my prior system and less time to set up.
As for time... it all depends. I think the time spent brewing on a GF is close to what I would have spent on my old system.