I've been running the 50-584 G-One Speeds for a couple of months now, so about 600-700 miles on 80% rough pavement and 20% gravel. Mine weigh 500gm on my scales and caliper 49-51mm wide on my HED Belgium+ rims, so pretty much as advertised. I bought them instead of the Compass 48-584's hoping for comparable (low) rolling resistance combined with better flat protection. My previous flat experience has been so-so with Compass and excellent with Schwalbe, although to be fair to Compass, my Schwalbe's have all been heavier belted tires.
The rolling resistance does feel comparable to Compass tires (in other words, very good!), but I had 2 flats in the first week of riding, and then one stubborn slow leak later on. This was discouraging, as I considered 6 flats per year as poor performance on my Compass tires. The flats may have been nothing but bad luck, but it makes me wonder how effective the belted construction is. Maybe the belt is very thin, as it doesn't seem to hinder comfort or rolling resistance. Since the flats, I felt compelled to have my first go at converting the tires from tubed to tubeless (the process was actually easy). My first sealant was Stan's but there was one puncture that would not completely seal; it would scab over but eventually start leaking again, spraying sealant all over the place. I finally got smart and changed to Orange Seal, and for the past month, the tires have been great.
In summary, the G-One Speeds are good tires, but I'm still wary after some bad luck in my first month of use. I'm not sure if they are worth the weight penalty over the Compass tires (87gm x 2 tires), given that the belted construction hasn't been very effective for me. I also wonder about tread life, as the tread seems pretty thin. So a slightly less than glowing report from me, but I really have been enjoying these tires lately.
Jack
Seattle