I know the local Hyosung Dealer here in Halifax and am very familiar with the GV250 Aquila 250 cruiser and GV650 Aquila 650 power cruiser.
They have sold about 50 250's and about 15-20 650's in the past 3 seasons, so my thoughts are based on a fairly large sample size. I have talked with several of the owners and observed the bikes being sold both new and used.
Both are really good bikes.
The 250 cruiser is a strong alternative to other "beginner" bikes because it has a larger chassis, wheels, tires, etc compared to other "beginner" bikes.
A full-sized person can ride one comfortably, and two adults can ride two-up on the GV250 all day long at highway speeds without effort or being scrunched up.
They are priced well, especially used.
I am not aware of ANY problems with them...they have a great warranty which is transferable, but it is very rare for the GV250 to have a problem.
It's a lot like a Honda that way.
The only known "weakness" in the GV250 is they use a cheap battery and because Hyosungs sit longer in showrooms before being bought than many other brands, the battery sometimes arrives weak....but a crappy battery is a minor issue.
The 650 goes like stink, has floating rotors, alloy wheels, a fork brace and a whole bunch of "quality" features you don't often see on bikes in their price point.
Also, because Hyosung builds motors for Suzuki under contract, the 650 is VERY similar to the Suzuki 650 v-twin, though not a flat out clone.
The ONLY issue I'm aware of with the GV650 is the kickstand starter interrupt switch goes bad due to road grime quicker than other similar switches...this is an issue also familiar to Suzuki 650 twin riders in my observation and is easy to replace yourself, or under Warranty or just bypass the danged thing.
As a used bike, Hyosungs are usually a great deal because the Name doesn't have much traction in the market yet.
Carb Hyosungs (the newer ones are EFI) have no issues with the carbs.
Some early versions of the electronic LCD gage pods are prone to kakking out at a young age, moreso on the 650 than 250. The pod was replaced a couple of years ago with more conventional looking gages.
Parts are often slower to get than with bigger brands, mostly because the dealer network consists more of dealers that are starting out or small compared to bigger money businesspeople who run other dealerships.
Hyosung in Korea is run by the guy who grew HJC Helmets from nowhere to recognition in a few short years, so it's a well-run company, about 40 years old and their bikes are very well-thought-of in southeast asia.
Nothing wrong with a Hyosung, decent bikes...but if the North American Market doesn't warm up to them, you could get caught with an orphan, so best to buy one used and for a low price.