Flash itself is widely used to write websites that can be accessed by different internet browsers, it is therefore an easy way to write malicious code if you host a malicious website. For sites like channel 4’s player it should be ok
I personally set my browser to prompt to run on a use by use basis, rather than its default always alllow:
https://www.tomsguide.com/us/flash-click-to-run-how-to,news-20422.html
I know IT support folk that don’t trust it and disable it completel across entire networks, and some that are quite happy with it...