Ok, I acquired the G9100TC (below) a bit over a month ago and set the time based on my dad's exec waveceptor model (WVQ600DCA-2AV) which had synced the night before, and then I compared the times again one month later to find that the Gulfman had only added 3 seconds to the fully synced waveceptor's time. Only 3 secs out, or a bit over 1/2 a minute a year!!!
That's a hell of a lot better than +/-15 secs a month.
I should add that I don't use the el backlight or alarms...I don't know if that affects accuracy or not.