I am currently using them and purchased them from Amazon.  They offer both 2 in 2 out and 2 in 3 out.  I have tried multiple styles and they all work however the recent box I bought (Gkeemars) work and mount the best. They seem to be better made also.  I use them on Block sub-Bus's where I know I will be using CT's for monitoring as it's easy to disconnect a wire to slip them on.  For mains to sub-bus's I use the 3M suitcase style with spade connectors. Maks it easy to disconnect for troubleshooting.