Q: Is it fast enough?
A: As with any browser-side work you do, the profiler is your friend. The value system (see Q: How are floats vs. ints handled?) adds a fair amount of overhead, so you may find that the equivalent code written in vanilla JS is faster than writing the same logic in PHP and transpiling it down to JS with Uniter.
Q: How are floats vs. ints handled?
This means you can take a package that already exists on Packagist (like a Symfony component), install it with Composer and use it browser-side too.
See the Composer autoloader section for an explanation of how this works.