Optimizely is now focusing on the enterprise segment, which requires a different culture and skillset than you'd need when selling to smaller businesses. Doing both at the same time, for most products, will almost always require two separate cultures, which is difficult to maintain (unless you're a giant corporation with different departments). An exception to this rule may be Slack, where price points grow linearly with company size.

In website testing, specifically A/B testing, the enterprise segment is likely more valueable as smaller customers tend to exhibit vastly higher churn rates. Also, a 1% increase in conversions will translate to millions in incremental revenue for established companies, making it much easier to justify higher price points.

As for which pricing strategy works better when working towards an IPO, it seems that the data doesn't favor one approach over another: http://tomtunguz.com/no-mans-land-saas/