Recs.
Updated
SpecsUpdate
Pros
Pro Transparent & permissive licensing - no strings attached
From https://about.draw.io/pricing/ :
" draw.io online is a free-to-license web application for everyone. It is completely free to use for any purpose, there is no premium pay-for functionality, watermarking, or other limitations. You own the content you produce with draw.io and may use it for any purpose, including commercially. We don’t sell your personal information or data. We don’t store your data. You own your data and the application is open source.
The exceptions to draw.io being free are listed below, these are how draw.io is funded."
Super-simple Terms of Service - 1 page with no nasty strings attached.
This is enabled by the developers having a great business model.
(These seem like they're different pro's, but they're all interlinked)
Pro Supports version control and revision history for drawings
According to the online user manual. This apparently includes version control when documents are hosted in Dropbox or Google Drive.
Cons
Con Online User Manual good, but not completely comprehensive / intuitive for quick searching
e.g. it makes no mention of templates when using the search tool for seemingly obvious terms like "template", or specific types of diagram (e.g. Venn, Gantt, etc), but upon searching Draw.io's interface, it seems that it is possible to cobble something up to make something like a Venn diagram without having to start completely from scratch. It's probably possible to find this out by working methodically through the User Manual, but that may not suit those who want to answer a specific question quickly. So, you need to be patient and step through the User Manual.
Con Introductory explanation on draw.io homepage doesn't appear correctly
It may be due to a browser setting/add-on, but when the draw.io homepage is loaded in Firefox, the product overview appears only very briefly and is replaced by a box asking the user to nominate where they want to save their files. As such, the website is not as self-explanatory as it should be, and links to usual website information/links like Home, About Us, Project Overview, etc. are not immediately obvious. These are found under the "Help" menu, but this is presented in the convention of a menu from a traditional desktop program rather than a website, which some users may find confusing / not apparent.
Con Pre-built templates for common diagram formats not extensive, nor inuitively found when quickly "diving in" to draw.io as a naive user
Searching within Draw.io for templates for common formats (e.g. Venn diagrams) yields no results - as it stands, it seems to be necessary to make the diagram yourself from scratch, rather than tweaking an existing template or merely adding text to it. Some sort of "Template Wizard" would be helpful.
Con Login attempt sometimes fails when trying to sign in via Google account
With an error message: "Log in attempts failed. Please try again later".
Fortunately, Draw.io's support forum has some suggestions for troubleshooting this.
As it turns out, it's possible to work around this error message by signing up for an account directly with Draw.io, which is very simple to do, with seemingly no strings attached.