We fitted them on our Hobie Tiger. You can swap out the stock Harken swivel block & cleat system and reuse the bracket riveted to the mast. They seem to work well enough - very easy to release under load. The Swivel units use the regular small spinlock surrounded by a resin bracket - so it is easy to replace the unit when the teeth on the cam wear out (as they will do).

Our local group found that small spin locks seem to wear out fairly quickly. They may only last a season of heavy use. The weak point seems to be the serrated surfaces that grip the line. Perhaps they need to change to aluminum from the resin material used at present.

Chris.