I'm using them successfully in places where friction is not a major issue - sheet spans and downhaul spans, where there is just small readjustment of lengths and angles. I also have the largest model in place of the sheet block that's up in the air, as it's lighter and doesn't hit me or the boat so hard when I lower the sail, but there is more friction than a good block. In the rest of the sheeting system, I use Garhauer ball bearing blocks, for minimum friction, so I can allow myself the extra friction of just one ring, as a trade-off against lightness. I wouldn't ever use them on a halyard, where friction does matter.