Just recently (like 2 months ago) I had the task to evaluate proper OSS replacements for the main charting of a client. So far, they've used a paid solution - but there have been a couple of reasons why the wanted to migrate.

Needless to write that eCharts was the clear winner. Not only is it greatly customizable, fully feature complete - it also had similar performance data as their paid solution. And performance matters as their largest chart has around 300k data (we discussed and could maybe be satisfied with 80-100k as well - but for most OSS charting libs even that would be pretty much impossible to render quickly).

For everyone who is looking for something super easy and quick it might not be the best solution (personally I like Chart.js in this area the most), but if you want a charting solution that out of the box is fast and comes with everything you might ever need then eCharts is for you.