From what I read he said he took it down as there was some security issues and he fixed it and will release a new one for 4.0.0. But if you want to swap then you have to either edit the database for the service_fields and remove unwanted rows / options per service and change if needed to since the names will be different or build an importer plugin.
Hi there, there's no official importer for ClientExec at the moment, I have imported a client over before which took about 2 days but it was a manual job. The other option is to import to whmcs and then to Blesta.