The Exodus Twin Pack carrier locks up to two bikes to the rack and the rack to your roof bars, and it is cost effective.
One lock secures the mounting plate to your roof bars, with plenty of adjustability on the distance between the bars – although the clips will only accommodate standard square-profiled bars.
The main clamp jaws have a soft rubber liner but the QR-style lever of the locking handle only opens them by a relatively small amount. The tapered shape of the jaws and the QR system to open/close them mean it can be a fiddle to get them open enough, something that could have been designed out with a more generous cam or different jaw shape.
Each holder (sold as part of the Twin Pack) weighs 2.8kg.