I am Ramesh from Zoho. Thanks for writing about Zoho. Regarding your specific points:

1) iframes: Yes iframes is the best option currently as it will always have the data currently available in your Zoho spreadsheet. Probably in the embed code that we give out, we can put a text element (outside of the iframe) linking to the public spreadsheet. This way, while reading in feed readers, they will atleast get a link to the spreadsheet if not an iframe.

2) No updating: The content in the iframe does not live update in real time, but whenever the iframe / page reloads, it brings the current up-to-date content available in your Zoho Spreadsheet.

3) Reliability: We are working hard to make our services as reliable as possible.

Regarding the third decimal place, you can increase the decimal place of the numbers in your cells as described in this forum post.

Regards
Ramesh