I've had my 2010 EFi GT650 for 6months or so after trading up from the carb'd GT250 model (the bike is an ex press/demo bike) and I've been thoroughly pleased with it so far.
Build quality is pretty good compared to older examples and seems to be getting better each year, though they don't like to be stored outside of a garage under a bike cover, as with mine corrosion is starting to show in some of the welds.
The fuel injection on my bike (Mikuni throttle bodies) is ok but doesn't like to be under load at under 2,000rpm. Later models seem to be better though.
Ride quality is pretty good with the adjustable forks and it holds the road pretty well in the twisties, but the seat is definitely sport bike hard and not great for touring on. After about 2hours solid riding on the highway I HAVE to get off and rest.
Range is hard to gauge as probably the most annoying aspect of the Hyosung is the fuel gauges have never been very accurate, reading almost empty with over 4L left in the tank.
It is a bit heavier compared with its contemporaries too and of course has a very limited steering lock which makes navigating slow speed obstacles challenging.