Open Sans is a horrible font, is there any chance that you could change the default font to something even remotely better? It is SO narrow and small, it's nearly impossible to read at normal sizes.
Further, it does not look the same in the editing mode as it does in the preview/run mode, which means you can't really plan spacing well.
Here's what it looks like (Macbook Pro on 27" retina display):
bad version
Here is the font in edit mode (and, what it is 'supposed' to look like in normal use):
good version
Hi, Mike.
We are considering more options for fonts. May be web fonts, so that when the prototype gets shared, users will also be able to view the correct font if they don't have it installed. However, depending on the browser used, there may be some differences in the font rendering.
Can you expand on what you meant by narrow so that we understand the issue like you do? Is there a better font we should consider? We haven't noticed issues with readability when testing prototypes here, and that may be why we were unaware of any font readability problems. But then no prototypes are alike, and you may have specific situation that we should follow up on.