Its implementation is not different from reference and it isn’t bad in any way.
There are not many alternatives out there. Native SMAA would be pretty good indeed, but if you search the forum, you will find a thread about integrating SMAA into the engine.
I haven’t seen FXAA perform any kind of wonders, that would not be expected from it.
Perhaps you should take a look at a paper, that explains how to fine-tune FXAA to your project needs.