Except Google Optimize will be free[1]. There's services that I've used with free plans that I later upgraded to paid plans (Mouseflow and Gleam.io come to mind), just because I knew I wasn't going to be hassled after a 14 or 30 day trial. Sadly that is not the case with Optimizely. I would personally wait for Google Optimize to come out of beta.

1. https://www.google.com/analytics/optimize/compare/