I had a Hyosung 250cc cruiser with the same engine as the GT250.. I had no problems with parts or service. If there is a dealer/service shop near you, I wouldn't worry about that.
I would have loved to have the Comet 250R over the GV250, looking back now. The engine was smooth as silk, no unwanted vibrations. It was quick around town, and I got up to 80mph without any trouble.
The new GT250Rs have been dynoed at 23.6 rwhp, (
http://www.hyosungmotors.com.au/AMCN_DEC_05_GT250R.HTML) which isn't too far off from the Ninja 250 (which is around 26 rwhp). The torque curve is also very flat, which leads to extremely predictable power delivery.
The GT250R should be a little quicker than the GV250 I had, as it is tuned more aggressively.
If you like the bike, I wouldn't shy away from it just due to the brand. A lot of people are buying Hyosungs now, and while you might have to wait a couple days for parts to come in, there shouldn't be any problems with not being able to get parts or service!
I liked my Hyosung, and I would get one again if the situation arose. I wouldn't mind a GT250R for a commuter bike.. I got 65mpg on my GV250 around town, even higher on the highway.
For reference, I'm 6'0 and 235ish lbs... and I still enjoyed riding the 250 around. If I would have gotten the Comet and not the cruiser, I probably would have hung onto it... but I decided that I don't care for the cruiser seating position.