With the latest three.js update (r180) the use of the Spark GPU codecs is now straightforward and integration into existing gltf loaders requires just one line of code.
This blog post outlining the few steps involved, goes over some of the surprises I encountered, and takes a close look at performance.
The spark.js GitHub repository now includes three.js examples that are trivial to run, just:
``` npm install npm run dev ```