What Excel formats do you support? I tried a simple Excel 97-2003 .xls, with no VBA or addins, and got some kind of format error.
Can I also suggest you let folks play around without having to create an account (I abandoned at that point so haven't been able to play around), or at least provide a demo account that mops up stuff older than 24 hours.
Excel with multiple worksheets is on the roadmap. Wanted to get the leanest solution out first to better gauge interest.
There is a link to a live API on the homepage, and a playground on the API's page which you can use by hitting "Free Token" up top.
The copy and placement of those buttons needs to be cleaned up to be conveyed better.