Khan is awesome. And if we end up building our own curriculum we will likely be using it for math. It doesn't seem like the one-stop shop we would like though.
(US Edition since you're in Utah. US Ed converts spelling to US and some of the units to non-metric, so students practice with both metric and non-metric units instead of metric only. Standards Ed is just as good as US. It is same content as US Ed but reordered somewhat to match pre-Common Core CA system. I'm guessing Common Core is another re-ordering of the same "Primary Mathematics" content. If so, it should be equally good. They no longer use this in Singapore for reasons that relate to integration with their non-math curriculum, but that is not relevant to someone using this as a purely math curriculum.)