Sb10,
It is possible that no one has answered regarding trial periods because it has been asked and answered a couple times. Although, those threads are gone due to unnecessary drama --threads full of accusations and paranoia... Im sure a few of the HD owners, Including myself, would like to avoid that happening again --so I can have a place to hear more about them, as well as comment on further once the cables I have purchased are fully broken-in (slow process on my part these days).
Maybe just shoot WorldWideWholesale(s?) an email and ask directly. They are the NA distributors of HiDiamond and can answer when and where you may be able to find them in your area, or help you with a purchase...
As far as comparisons... Do a search for this brand here and you will see a few brands people have used before settling on the HD's.
Personally, I do not feel I have tried enough PC's to commented further. But the HD PC I have has fit wonderfully into a mix of Wywires, TWL and Sablon. When I can though, I will begin to replace... Although, there are others that have replaced MUCH more expensive cords than I have.
The Power3 is the first 'no trade-offs' PC I have had in my system. I love it and want more.
I hope this helps you some.