Yes, I'm very grateful that Ryan has been a part of the team for both papers- his expertise has been a tremendous asset! To answer your question about the differences between tools:
LocusZoom.JS is the basic rendering library. It can be highly customized, but you need to write your own code to use it with your own data.
LocalZoom (and
my.locuszoom.org) are the "glue code" required to make plots with your own data. They handle opening files and parsing into a form the web browser can read. Some websites, like the t2dkp, have their own way of fetching data; they use locuszoom.js as a separate piece.
LocalZoom operates on local files, and is especially aimed at people who don't want to trust uploads to third party server. It does not summarize the file because it does not read it all at once into memory; this would be slow and might crash the web browser.
Eventually I'd like to add "plot multiple tracks" to
my.locuszoom.org, but since it would ideally use a mix of personal and third party datasets, we will want to improve the search and metadata features first, so that we don't suggest tracks that are not of interest. (Some of the public datasets shared by users at present have titles like "aaaa", which would be a bad user experience)
For your tabix question: PLINK is an interesting program, in that widely used versions like 1.9 often create space delimited files; tabix requires a tab delimited format.
My.locuszoom.org handles file conversion for you and someday we will add space delimited file support; for localzoom this is harder because it does not convert the file, and the limitation is in a separate tool (tabix).