Gapless 5 has a built in UI and style. Our library is headless: you bring your own UI and controls. It just depends on what your use-case is.
The problem with exclusively using the web audio API is that the entire track must be loaded into memory before playing it, whereas HTML5 loads progressively. So we use both to balance the techniques.
In prior versions of the library, we'd load the track in parallel to HTML5 and make the switch mid-track so it's actually far less noticeable even if it does blip. I'm considering adding that to the new version.
Another alternative is building a custom buffer using RANGE requests to exclusively drive it via the web audio API. But obviously that is a far more complex undertaking (and requires the server to support RANGE requests). I'm open to implementing it, though.