Be careful about the claimed specs of "15-35Khz". I've seen several monitors listed like that (particulary when its not the original manufacturer info) when it should really say 15,31-35Khz. ie its not the full range.
I have something similar but the 15Khz is supported on a seperate input.
re: 31Khz with scanlines vs 15Khz. I've not tried for ages, but it doesn't look anywhere near as good at 31Khz. I have no idea why. If there was no difference, people would not bother with arcade monitors/ArcadeVGA.