I have no concerns at all about using the Searchable Plugin, as long as you don't use it. Compass hasn't been updated for 5 years. The plugin is not maintained, the documentation is spread over the Grails site, and there are issues when deploying an application using Searchable.
I would not recommend using this plugin at all, but use something like Elastic Search or MongoDB search instead. It seems the ElasticSearch plugin has recently been revived (
http://grails.org/plugin/elasticsearch), so it might be worth checking that one out (or contributing to it ;-)