It very much depends on the weather and experience of the group members.
The North Ridge of Tryfan is not technically difficult, but if any members of your group party, dislike heights and exposure, its not the best route to take them on.
You should not really require a rope, and the scrambling is not that technical, but the exposure on the ridge itself, is quite severe, not the place to take novice walkers afraid of heights.
Its also requires careful navigation, as its very easy to stray off the main ridge itself, and find yourself on difficult and challenging rock, so it might be a good idea to take a rope, just as a precaution.