TextMesh Pro FastAction questions

TMP comes with various FastAction classes. The name suggests it's faster than using System.Action, but looking at the code, it uses System.Action internally.

It seems FastAction is a layer on top of System.Action, but why?
Do you have numbers how much faster it is?
Is it safe to assume to use FastAction over Action always?
Are there cases where using Action is more benefitial than using FastAction?

 

Those were implemented a long time ago as an alternative to using delegates which are immutable where using += operator generates allocations as the delegate list is recreated.

Essentially it consists of replacing the raw delegates with wrapper classes that can handle registering to delegates and removal of them in constant time instead of linear time.

This implementation was the contribution by a TMP user back then

 

I see, thanks for the quick response!