I have owned the Frey balanced interconnect. I didn't recall huge changes after the burn-in period but it did possess a slight tilt in the treble that some can associate with brightness or harshness. The Frey does have great resolution and detail and will match well with darker sounding components. It would be weird if higher-end Norse series of cables sound harsher than the lower-end as it should be the other way round. I have not tried the Heimdall so I cannnot comment.
