The reasons this isn't a toggle on the textmesh/sprite is twofold:
1. Having an Update function increases overhead significantly, so having it only where absolutely necessary is a lot better.
2. The animation system can't update C# properties. For this, in the most trivial case, then a script like this works perfectly, but if you are animating a hierarchical character (eg. a skinned character, or entire UI) then this script is a lot more efficient, as it only has one Update function for all its children.
What I'll be doing -
1. I'll be adding an AutoCommit for usual use cases, i.e. from script. This can be done without an Update function.
2. I'll find this script I wrote and add it to the distribution as in a "Goodies" folder or something like that.