Eh, these are easy fixes. We're making progress daily on making it feel more "native" (i.e recently added present/dismiss animations). Try the demo[0] in your mobile browser, should feel pretty smooth. We've tested extensively on a whole range on devices and performance wasn't an issue. It's really the animations (or lack thereof) that make or break perception of "jankiness." What we have now is our first solid functionality-oriented release; next releases focus on tidying up the edges.
[0]: https://standardnotes.com/demo