Edited to add: CAT is now working. The latest sysfloat CAT can be found here. If anyone has trouble getting CAT to work, (via error messages etc) please post your Mac model, model card or dongle. Make sure you have a recent backup before going through the process, just in case something untoward happens. Thanks to Scoobie for working to help debug the older CAT problem with Handoff, and to Sysfloat for keeping CAT abilities alive for us and refining the install process.