One thing important to note is for certain use cases of Optimizely like A/B testing, it's actually desirable to block rendering until it's initialized as otherwise you end up with a flash of the default variation that then gets switched to the appropriate one afterwards.
Though after working with a few of these A/B testing vendors, I'm firmly convinced that you'd be better off long term implementing your own A/B testing service on top of some internal admin UI builder like Retool.
Though after working with a few of these A/B testing vendors, I'm firmly convinced that you'd be better off long term implementing your own A/B testing service on top of some internal admin UI builder like Retool.