The ability to see who has seen what is one of my favorite features that makes this service so effective for us! There are other services out there, but I wish they had these type things sooner (or at least as an add-on.) Great customer support from both technical AND nontechnical folks when we have questions or problems--even after several years in operation their staff still knows how best use it's resources within our organization.--We're using them mostly internally now instead of through any sort of work/external collaboration site like Slack or HipChat; not sure why? Perhaps because most people don't realize just HOW good this tool really can be unless you've used something else first before trying again?? We were having some issues keeping track of project information among multiple internal teams which could lead into miscommunication about deadlines / progress etc., plus also made life easier if someone was away without being able to communicate easily via email since all communications would go directly back up via.